EXCHANGE 


EXCHANGE 


Studies  in  Adsorption 


A  THESIS 


SUBMITTED  TO  THE  FACULTY  OF  THE  GRADUATE  SCHOOL 

OF  THE  UNIVERSITY  OF  MINNESOTA 
IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 

FOR  THE  DEGREE  OF 
DOCTOR  OF  PHILOSOPHY 


BY 


EARL  PETTI  JOHN 


June,  1918 


Studies  in  Adsorption 


A  THESIS 


SUBMITTED  TO  THE  FACULTY  OF  THE  GRADUATE  SCHOOL 

OF  THE  UNIVERSITY  OF  MINNESOTA 
IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 

FOR  THE  DEGREE  OF 
DOCTOR  OF  PHILOSOPHY 


BY 


EARL  PETTIJOHN 


June,  1918 


•  •      «     t. 


Studies  in  Adsorption 

PART  I.— AN  ATTEMPT  TO  DETERMINE  APPROXIMATE 

GRAIN  SIZE  AND  THE  MEASUREMENT  OF  THE 

MAXIMUM  THICKNESS  OF  SURFACE  FILMS. 

Introduction. — The  determination  of  mean  grain  size  is  of  importance 
in  a  number  of  problems.  Among  these  are  problems  involving  the  flow 
of  water  through  soil  and  adsorption  problems.  In  the  first  case  grain 
size  determines  the  number,  size  and  kind  of  pores  through  which  the 
water  flows,  in  the  second  it  determines  the  amount  of  surface  available 
for  adsorption.  In  the  former  case  King1  has  done  some  work  on  esti- 
mating pore  space  and  relating  the  rate  of  flow  to  the  diameter  of  the  grain; 
in  the  latter,  mass  is  universally  substituted  for  surface,  a  procedure  which 
is  apt  to  introduce  a  variable  error.  The  first  part  of  this  paper  deals 
with  a  new  method  of  estimating  the  diameter  of  small  grains  and  gives 
results  for  materials  of  known  surface. 

The  thickness  of  water  films  formed  on  glass  and  sand  has  been  investi- 
gated quite  fully.  The  second  part  of  the  paper  describes  a  simple  method 
of  determining  the  maximum  film  which  can  form  on  materials  of  this 
kind. 

Materials. 

Sand. — Ordinary  river  sand  was  used.  It  was  treated  with  con- 
centrated hydrochloric  acid  until  no  test  for  iron  was  shown.  The 
acid  was  then  washed  out  with  distilled  water  and  the  sample  dried  in  the 
air.  Four  samples  were  obtained  by  sifting.  The  first  sample  contained 
all  of  the  sand  which  passed  the  ten-mesh  screen  but  was  retained  by 
the  twenty-mesh  screen.  The  second,  third  and  fourth  samples  consisted 
of  the  fractions  from  the  original  lot  retained  by  the  forty-,  sixty-  and 
eighty-mesh  screens,  respectively.  These  are  called  ten,  twenty-,  forty-  and 
sixty-mesh  sands  in  this  paper. 

The  grains  in  this  lot  of  sand  were  far  from  spherical,  no  two  diameters 
being  the  same.  An  approximation  of  the  surface  was  obtained  by 
weighing  a  counted  number  of  grains  (4000  to  5000),  to  get  the  average 
weight  per  grain,  and  determining  the  specific  gravity.  On  the  assumption 
that  the  grains  were  spherical  the  diameter  and  surface  of  a  single  grain 
could  be  calculated.  It  was  realized  when  these  values  were  obtained 
that  they  were  at  best  only  approximations. 

Ottawa  Sand. — A  single  sample  of  sand  called  in  this  paper  "Ottawa 

Sand"  consisted  of  well  rounded  grains.     This  sample  gave  values  by  the 

above  mentioned  method  which  were  very  close  to  the  true  value  for 

the  diameter  and  surface.     It  was  considered  to  be  of  known  surface. 

1  Nineteenth  Annual  Report  Geological  Survey,  1897-98,  pages  67-294. 


444249 


Glass  Pearls. — The  glass  pearls  used  were  solid,  round  and  of  various 
sizes,  as  indicated  in  the  table  below.  A  few,  which  were  poorly  formed 
were  removed  from  the  lot  by  rolling  them  down  an  inclined  board.  Those 
which  were  not  round  could  be  easily  picked  out  in  this  way.  The  pearls 
were  from  two  different  sources,  and  apparently  of  different  kinds  of  glass. 
They  differed  considerably  in  specific  gravity. 

The  first  lot  was  purchased  retail.  The  material  was  sold  under  the 
name  of  "glistening  dew"  and  was  used  to  decorate  fancy  cards.  Two 
samples  were  obtained  from  this  lot  by  "elutriation."  A  quantity  of  the 
pearls  were  placed  in  a  tube  and  delivered  from  it  at  a  slow  rate  into  a 
rising  column  of  water.  Under  these  conditions  by  properly  regulating 
the  current,  the  lighter  ones  were  carried  up  and  the  heavier  ones  sank 
to  the  bottom.  These  samples  are  No.  9  and  No.  10,  in  the  tables. 

The  second  lot  consisted  of  five  samples,  Nos.  i,  3,  5,  7  and  8.  The 
individual  pearls  in  each  sample  were  of  the  same  diameter  except  for 
No.  7  which  contained  pearls  of  two  sizes.  These  samples  were  obtained 
from  Germany  and  when  received  were  coated  with  dye. 

All  of  the  samples  were  cleaned  by  boiling  in  concentrated  nitric  acid, 
washing  free  from  acid  and  air  drying.  The  diameter  surface  and  volume 
of  the  pearls  in  each  lot  was  determined  by  the  method  used  for  the  sand. 
Since  the  pearls  were  very  nearly  spherical  in  form  they  were  considered 
to  be  of  known  surface. 

Precipitated  Silica. — Precipitated  silica  was  only  used  in  the  preliminary 
work  in  this  paper.  No  attempt  was  made  to  determine  the  surface  or 
diameter  of  the  particles  of  the  powder  accurately.  The  microscope 
showed  it  to  be  very  fine,  but  far  from  uniform.  The  sample  used  was  of 
German  origin.  It  was  necessary  to  wash  free  from  iron  before  using  it. 

The  following  table  gives  the  weights  and  the  specific  gravities  of  the 
materials  used. 

TABLE  I. 
Data  on  Materials  Used. 

Samples.  Mean  weight  of 

Sand.  single  grain  in  gram.  Specific  gravity. 

io-mesh  0.000168  2.643 

2O-mesh  o.ooono  2.645 

40-mesh  o .  000030  2  . 650 

6o-mesh  o .  000007  2  . 666 

Ottawa  o .  000686  2 . 656 

Pearls  

No.  i  0.003988  3-101 

No.  3  0.002625  3-090 

No.  5  0.000853  3-079 

No.  7  0.000261  3-125 

No.  8  0.00012 1  3-069 

No.  9  0.000182  2.505 

No.  10  0.000122  2.496 


Part  I.  —  General  Considerations. 

There  are  at  present  three  methods  of  determining  the  surface  of  small 
grains.  They  are: 

i  .  Count-weight  Method. 

2.  Average  Diameter  Method. 

3.  King's  Method. 

The  count-weight  method  has  already  been  described,  it  being  the 
method  used  in  the  calculation  of  the  diameter  and  the  surface  of  the 
samples  used  in  this  piece  of  work.  It  is  accurate  only  if  the  particles  are 
spherical  and  of  the  same  diameter. 

The  average  diameter  method  consists  in  measuring  the  diameter  of  a 
large  number  of  grains  and  using  the  average  obtained  for  calculating  the 
surface  and  volume.  It  will  also  give  accurate  results  if  the  grains  are 
spherical  and  of  very  nearly  the  same  diameter.  This  method  as  well 
as  the  former  one  may  give  results  far  from  the  actual  ones  for  grains  that 
are  not  spherical. 

King's  method  consists  in  determining  the  time  taken  for  a  given  volume 
of  air  or  water  to  pass  through  a  certain  packed  volume  of  the  material  to 
be  tested.  A  formula, 


is  given  for  the  amount  of  air  flowing  through  the  apparatus  in  a  given  time. 
The  quantity  for  unit  time  varies  with  the  square  of  the  diameter.  The 
method  is  a  first  attempt  to  determine  diameter  and  surface  independent 
of  the  individual  particle.  The  above  equation  is  derived  from  a  mathe- 
matical study  of  the  factors  involved  in  the  passage  of  air  through  such 
a  medium.  The  equation  and  the  experimental  results  reported  by  King 
check  with  a  fair  degree  of  accuracy. 

The  method  described  in  this  paper  is  in  some  respects  similar  to  that  of 
King,  the  results  being  derived  from  the  rate  at  which  water  is  removed 
from  the  surface  instead  of  the  rate  at  which  air  passes  through  a  mass  of 
packed  grains. 

Experimental  Work.  —  The  first  work  done  was  of  a  preliminary  nature 
and  was  carried  out  for  the  purpose  of  determining  the  magnitude  of  the 
changes  that  could  be  expected  with  the  materials  used. 

Air  dry  samples  of  Ottawa  sand,  ignited  and  unignited  silica,  and  twenty-, 
forty-  and  sixty-mesh  sands  were  placed  over  phosphorus  pentoxide  to  dry, 
being  weighed  at  intervals.  Seventy-five  gram  samples  were  used.  The 
samples  were  placed  in  crystallizing  dishes  all  of  them  being  placed  in  the 


same  desiccator  to  insure  their  drying  under  uniform   conditions.     The 
results  obtained  are  shown  in  Table  II,  and  on  Plate  I. 

A  second  series  of  determinations  was  then  made  by  placing  weighed 
samples  of  precipitated  silica  (air-dry),  over  different  concentrations  of 
sulfuric  acid.  The  desiccators  in  which  the  samples  were  subjected  to 
the  vapors  of  the  sulfuric  acid  solutions  were  themselves  placed  in  a  large 
oven,  electrically  heated.  Under  these  conditions  the  effect  of  tempera- 
ture and  vapor  pressure  on  the  film  could  be  studied  simultaneously. 

TABLE  II. 
Loss  in  Weight  of  Air-dry  Material  Placed  Over  Phosphorus  Pentoxide. 

Time  in  Ottawa  20-mesh  40-mesh  60-mesh  Ignited  Un ignited 

hours.  sand.  sand.  sand.  sand.  silica.  silica. 

I5/6  0.2  O.l8  0.12  0.09  0.05  0.05 

36/i2  0.34  0.32  0.23  0.15  0.07  0.06 

4n/i2  0.48  0.45  0.34  0.24  o.io  0.08 

6l/4  0.65  0.62  0.48  0.33  0.14  o.i  i 

73A  0.85  0.80  0.63  0.43  0.19  0.14 

iol/z  ....  ....  0.63  0.28  0.18 

nVa  ••••  ••••  0-72  0.31  0.20 

Results  expressed  in  milligrams. 

TABLE  III. 
Variation  in  Weight  of  Air-dry  Silica  when  Temperature  and  Vapor  Pressure  are  Varied* 

Series  i. 
12%  Sulfuric  Acid. 

Temperature,  C°.                              Vapor  pressure.  Increase  per  gram. 

50                                               88.0  0.00408 

43                                               61.3  0.00540 

33                                               34-5  0.00729 
19                                               13.6 

Series  2. 

44%  Sulphuric  Acid. 

50                                             48.3  0.00242 

43                                               33-7  0.00257 

33                                               18.8  0.00267 

19                                                 8.0  0.00304 

Series  3. 

52%  Sulfuric  Acid. 

50                                           31.5  0.00040 

43                                             22. o  0.00080 

33                                             13-3  0.00090 

19                                               5-5  0.00150 

Series  4. 

70%  Sulfuric  Acid. 

50                                             5.9  — 0.00170 

43                                               4.3  — 0.00180 

33                                               3.0  — 0.00180 

23                                                 1.6  — 0.00170 


On  removing  a  sample  from  the  oven  for  weighing  it  was  allowed  to  cool 
to  room  temperature  in  the  air.  Since  the  sample  was  at  a  higher  tem- 
perature than  that  of  the  room  no  accumulation  of  moisture  could  take 
place  on  it  from  the  air,  and  any  loss  of  moisture  by  it  to  the  air  would 
of  necessity  be  considered  as  condensed  moisture,  and  not  as  a  part  of  the 
surface  film.  Reheating  was  continued  at  the  same  temperature  until 
a  constant  weight  was  obtained.  If  the  weight  of  the  sample  so  treated 
is  greater  than  the  weight  of  the  air  dry  material  some  moisture  has  been 
taken  up  which  is  not  lost  during  cooling.  This  moisture  may  be  consid- 
ered as  a  part  of  the  semi -permanent  film  on  the  surface  of  the  grain. 


4.  Q  8 

Time  in  hours 


e 

.  & 

0 

i 
1 

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1  PLATE! 

.     Relation  between  vapor 
^  v      pressure  ana  increase 
^kf       in  ireiaht 

/ 

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^ 

§v 

/s 

7~ 

£: 

V. 
m 

4/ 

5 
i 

-2 

/  // 

&^f^-7 

M| 

"              ™             40             60            to            IOC 

Vapor  Pressure 


If  on  the  other  hand  the  material  on  exposure  to  the  air  reverts  back  to 
the  weight  of  the  air-dry  sample  no  thicker  film  than  that  present  on 
the  air-dry  sample  can  be  formed  at  that  temperature.  Vapor  pressures 
greater  and  less  than  those  of  the  air  under  ordinary  conditions  were  used 
so  that  a  tendency  to  revert  to  the  air-dry  weight  could  be  checked  from 
either  side.  The  values  obtained  are  shown  in  Table  III,  and  on  Plate  II. 
Discussion  of  Results.  —  When  a  pile  of  small  particles  like  any  one  of 
these  samples  is  exposed  to  conditions  favoring  evaporation  of  the  surface 
film  of  moisture,  the  greater  part  of  the  moisture  must  evaporate  by  way 
of  the  air  spaces  between  the  particles  composing  the  pile.  If  the  particles 
are  of  the  same  shape  and  if  the  same  arrangement  of  particles  holds  in 
the  different  piles,  the  size  of  the  air  spaces  will  be  determined  by  the 
diameter  of  the  particles.  It  might  therefore  be  assumed  that  there  would 
be  a  direct  relation  between  the  size  of  particles  and  the  rate  of  evapora- 
tion. The  results  in  Table  II  and  the  curves  on  Plate  I  show  that  the 
relationship  holds  for  the  materials  used,  the  loss  during  a  given  interval 
decreasing  as  the  grain  size  decreases.  The  relationship  is  not  a  simple 
one,  however,  since  the  capacity  possessed  by  a  surface  for  holding  a  liquid 
film,  as  well  as  the  arrangement  of  particles  in  the  piles  may  differ.  That 


the  relationship  is  not  simple  for  the  three  samples  of  meshed  sand  is 
probably  due  to  the  irregularity  of  the  grains  and  the  resulting  irregular 
arrangement  of  them  in  the  pile. 

The  results  from  the  second  series  of  determinations  are  shown  graphic- 
ally on  Plate  II.  Solid  lines  connect  points  at  the  same  temperature,  while 
"broken  ones  connect  those  for  the  same  vapor  pressure.  No  attempt  was 
made  to  definitely  determine  either  the  shape  of  the  curve  or  the  actual 
amount  of  liquid  held,  since  the  purpose  of  this  part  of  the  work  was  only 
to  get  the  magnitude  of  the  change  caused  by  variation  of  temperature  and 
vapor  pressure. 

Samples  placed  over  70%  acid  showed  a  decrease  in  weight,  all  of  the 
others  an  increase,  over  that  of  the  air-dry  sample.  In  taking  the  warm 
sample  out  of  the  oven  and  cooling  it  in  the  air,  there  is  no  tendency  for 
the  moisture  in  excess  of  that  held  by  the  air  dry  sample  to  evaporate. 
If  the  air-dry  sample  has  the  smaller  amount  there  is  no  tendency  for  the 
sample  to  take  up  moisture  from  the  air. 

From  the  curves  it  may  be  noted  that  the  change  in  weight  of  the  film 
formed  over  any  one  concentration  of  acid  is  very  slight  as  the  vapor  pres- 
sure is  increased,  and  that  the  slight  change  is  in  the  direction  of  a  de- 
crease in  weight  with  increase  in  vapor  pressure.  The  amount  of  the  de- 
crease for  a  certain  increase  in  temperature  also  varies  with  the  acid 
strength,  being  greater  with  the  lower  concentrations.  This  is  equivalent 
to  saying  that  the  decrease  for  a  certain  temperature  change  is  greater  as 
the  vapor  pressure  is  greater. 

Heating  the  sulfuric  acid  container  would  have  two  effects.  It  would 
decrease  the  capacity  of  the  solid  for  holding  moisture,  and  it  woud  in- 
crease the  amount  of  vapor  present  in  the  air  and  available  for  the  forma- 
tion of  a  film.  The  effect  upon  the  solid  would  undoubtedly  result  in  less 
liquid  being  held.  Increasing  the  vapor  present  might  cause  either  an 
increase  or  a  decrease  in  the  amount  of  liquid  held,  depending  on  the 
intensity  of  the  force  which  holds  the  film  to  the  solid.  As  the  vapor  pres- 
sure increases  water  will  evaporate  from  the  sulfuric  acid  solution  and  may 
evaporate  from  the  film  already  present  on  the  surface  of  the  pearl  also. 
In  the  experiments  above,  the  resultant  of  the  two  effects  brought  about 
a  slight  decrease  in  weight  as  the  temperature  increaseed. 

The  results  indicate  that  the  thickest  film  that  can  form  is  formed  when 
the  temperature  is  low  and  the  vapor  pressure  high ;  also  that  the  amount 
held  gradually  decrease  as  the  vapor  pressure  increases  with  rise  of 
temperature.  While  the  results  shown  do  not  make  this  a  certainty, 
they  do  make  it  probable,  since  the  only  other  possibility  lies  in  the  curve 
for  one  strength  of  acid  (broken  line  curve  of  Plate  II),  showing  a  maxi- 


mum  at  some  temperature  below  19°  and  decreasing  again  for  vapor  pres- 
sures below  this  maximum. 

The  curves  indicate  quite  clearly  that  the  film  is  not  chemically  com- 
bined, since  the  amount  of  liquid  held  at  constant  temperature,  decreases 
with  the  vapor  pressure  of  the  sulfuric  acid  solution.  This  is  not  a  normal 
behavior  for  chemical  compounds,  which  lose  their  water,  if  the  reaction 
is  a  reversible  one  stepwise,  rather  than  at  a  gradual  rate. 

These  results  show  roughly  the  magnitude  of  the  change  when  a  part 
of  the  film  ordinarily  present  is  removed  by  drying,  and  also  the  effects 
that  may  be  expected  if  temperature  or  vapor  pressure  changes. 

The  results  as  obtained  were  so  small  that  it  seemed  impossible  to  get 
measurable  results  on  pearl  samples  of  known  surface.  A  few  trials  showed 
that  the  weight  of  pearls  used  would  have  to  be  at  least  150  grams,  and  that 
this  weight  would  considerbly  increase  the  time  required  to  obtain  equi- 
librium conditions.  The  fact  that  the  loss  in  weight  varied  with  the  size 
of  the  grain  was  used  as  a  basis  for  a  new  method  of  determining  surface. 

It  will  be  seen  from  the  work  already  described  that  the  rate  of  loss 
of  moisture  from  a  mass  of  sand  grains  varies  with  the  size  of  the  grain, 
and  that  the  larger  the  grain  the  greater  the  loss  for  any  interval  of  time. 
It  seemed  probable  that  the  loss  was  dependent  only  indirectly  on  the 
grain  size,  the  direct  factors  being  the  amount  and  the  shape  of  the  un- 
occupied space.  King1  in  his  investigation  of  the  flow  of  water  through 
soils  determined  the  amount  of  this  space  for  different  soils,  calling  it 
"pore  space."  The  following  formula  was  used  in  determining  it: 

Vd  —  W 

looVd 
in  wrhich, 

V  =  volume  of  sand  and  pore  space, 

d  =  density  of  sand, 

W  =  weight  of  sand  used, 

P  =  pore  space. 

For  rounded  grains  it  was  found  to  vary  with  the  size  of  the  grain,  be- 
tween 32%  and  40%  and  for  ordinary  soils  between  32%  and  47%. 

The  force  which  holds  the  liquid  in  the  spaces  existing  in  a  mass  of 
small  grains  is  physical  in  its  nature.  The  nature  of  the  surface  of  the 
grain  and  the  size,  shape  and  arrangement  of  the  pores  in  the  mass,  de- 
termines the  magnitude  of  the  force.  For  material  of  the  same  kind  the 
nature  of  the  surface  need  not  be  considered. 

If  spherical  grains  of  uniform  size  are  used,  and  if  they  are  arranged  as 
compactly  as  possible,  both  the  pore  space  and  the  liquid  held  in  it  are 
constant  in  amount.     The  rate  of  loss  of  this  liquid  should  depend  on  the 
1  Loc.  cit. 


10 

size,  shape  and  arrangement  of  the  pores.  If  each  sample  is  made  up  of 
spherical  grains  of  one  definite  size  it  seems  probable  that  the  shape  of  the 
pores  would  be  the  same  in  every  sample  and  that  the  size  of  the  pores 
would  vary  with  the  size  of  the  grain  composing  the  sample.  It  also  seems 
probable  that  the  arrangement  of  the  pores  would  be  the  same.  Whether 
this  is  true  or  not  there  is  a  relationship  between  the  size  of  the  grain, 
the  pore  space  and  the  rate  of  loss  of  liquid  from  the  pores ;  and  spherical 
grains  which  pack  so  as  to  give  a  constant  pore  space  should  give  results 
which  would  show  this  relationship  most  definitely. 

If  it  is  possible  to  determine  how  the  rate  of  loss  varies  with  the  diameter 
of  the  pearl  and  with  the  pore  space,  the  pore  space  can  be  calculated 
and  the  diameter,  that  is  the  effective  diameter,  of  the  grain  can  be  de- 
termined from  the  rate  of  loss  of  liquid.  For  spherical  grains  the  actual 
diameter  would  be  determined,  for  other  shapes  the  effective  mean  di- 
ameter from  which  to  calculate  the  surface. 

The  glass  pearls  and  Ottawa  sand  already  described  provided  just  the 
kind  of  material  needed  for  determining  this  relationship.  The  centrifuge 
at  once  suggested  itself  as  a  medium  by  which  the  liquid  could  be  removed 
and  a  method  involving  its  use  was  devised. 

TABLE  IV. 

Losses  per  Gram  of  Sample  on  Centrifuging. 
Ottawa  Sand. 


Time  in  mins. 

Sample  No.  1. 

No.  2. 

No.  3. 

No.  4. 

IO 

O.OoSl 

0.0087 

0.0083 

0.0084 

10-20 

0.0070 

0.0088 

0.0093 

0.0073 

20-30 

0.0082 

0.0090 

0.0085 

O.OOSO 

Pearls  No.  10. 

10 

O.OO8O 

0.0065 

0.0064 

0.0083 

10-20 

0.0064 

0.0078 

0.0062 

0.0070 

20-30 

0.0057 

0.0061 

o  .  0050 

0.0059 

30-40 

0.0056 

0.0059 

0.0050 

0.0055 

Pearls  No.  8. 

IO 

0.0040 

0.0039 

0.0046 

0.0045 

IO-2O 

0.0043 

0.0054 

0.0042 

0.0052 

20-30 

0.0047 

0.0050 

0.0047 

0.0049 

30-40 

0.0047 

0.0051 

0.0049 

.... 

Pearls  No.  7. 

10 

0.0046 

0.0042 

0.0056 

0.0058 

IO-2O 

0.0048 

0.0049 

0.0053 

0.0052 

20-30 

0.0042 

0.0046 

.... 

0.0045 

30-40 

0.0045 

Method  Used. — Porcelain  Gooch  crucibles  were  used  to  hold  the  samples 
while  they  were  being  centrifuged,  those  being  chosen  which  had  per- 
forations too  small  for  any  of  the  sizes  of  pearls  used  to  pass  through. 
They  were  as  nearly  the  same  size  and  shape  as  could  be  obtained.  A 


II 

weighed  sample  of  pearls  was  transferred  to  a  Gooch  crucible  and  distilled 
water  was  added  to  cover  the  sample.  The  sample  was  kept  covered 
with  water  while  100  cc.  of  water  was  passed  through  the  pearls.  This 
was  done  in  order  to  wet  the  pearls  uniformly  and  to  remove  bubbles  of 
air.  The  greater  part  of  the  free  liquid  was  then  removed  by  suction, 
the  Gooch  crucible  was  transferred  to  the  centrifuge  and  the  sample  was 
rotated  for  ten  minutes  at  the  rate  of  1000  revolutions  per  minute.  The 
crucible  was  then  removed  and  weighed  and  alternately  centrifuged  for  a 
ten-minute  period  and  reweighed  until  the  original  weight  was  obtained. 
The  weights  of  duplicate  samples  as  well  as  those  of  the  different  sizes 
were  varied  somewhat  to  see  whether  an  appreciable  effect  on  the  loss  in 
weight  would  result. 

Ottawa  sand  and  pearls  Nos.  10,  7  and  8,  were  used,  the  loss  in  liquid 
being  determined  for  ten  minute  intervals  with  four  samples  of  each.  The 
results  are  given  in  Table  IV. 

Discussion  of  Results. — In  considering  this  method  of  determining  the 
diameter  experimentally  there  were  five  factors  which,  it  was  thought, 
might  cause  results  to  vary. 

1 .  Size  and  Shape  of  Crucibles. — It  was  possible  to  select  crucibles  which 
were  of  practically  the  same  diameter  and  height.     This  source  of  error 
was,  therefore,  of  but  very  little  importance.     There  is  no  doubt  that  a 
difference  in  the  diameter  of  the  crucible  would  cause  the  weight  loss  to 
vary,  since  the  centrifugal  force  acts  over  the  section  of  the  crucible. 

2.  Number  and  Size  of  Perforations  in  the  Crucibles. — No  effort  was 
made  to  measure  accurately  the  size  and  number  of  perforations  in  the 
base  of  the  Gooch  crucibles.     It  seems  probable  that  they  would  have 
an  influence  on  the  rate  of  loss  of  liquid  unless  they  were  numerous  enough 
to  readily  take  care  of  all  of  the  water  driven  from  the  pearls  during  a 
ten-minute  period.     Apparently  such  differences  as  existed  had  no  effect 
on  the  relative  rate  of  loss  of  liquid. 

3.  Amount  of  Water  Present  when  Centrifuging  Began. — A  rough  at- 
tempt was  made  to  adjust  the  amount  of  liquid  when  centrifuging  began, 
through  the  application  of  suction  for  a  definite  time,  following  a  definite  pre- 
liminary treatment.      The  method  used  did  not  do  this  with  any  accuracy 
since  the  amount  of  liquid  held  by  any  one  sample  of  pearls  was  not  the 
same  in  any  of  the  four  determinations  made.     It  was  expected  that  this 
might  lead  to  larger  losses  particularly  during  the  first  period  of  rotation. 
That  it  had  no  such  regular  effect  can  be  seen  from  the  results.     This 
is  probably  due  to  the  fact  that  on  centrifuging  a  constant  pressure  is 
applied  to  the  pearls  from  the  surface  layers  down,  and  this  pressure 
effects  the  removal  of  a  certain  quantity  of  water  at  the  bottom,  independ- 
ent of  the  am  ount  of  water  actually  present  in  the  crucible.     It  was  found 


12 

that  after  the  first  centrifuging  the  top  fayers  of  pearls  were  practically 
dry,  and  as  centrifuging  was  continued  the  dry  layer  deepened  until  all 
of  the  water  was  removed. 

4.  System  of  Packing  the  Pearls. — There  are  innumerable  possibilities 
in  arrangement  when  a  mass  of  small  pearls  are  poured  into  a  crucible, 
and  the  pore  space  may  vary  greatly  with  the  method  of  packing  em- 
ployed.    It  seems  probable  that  the  greater  part  of  the  variations  found 
in  the  above  results  are  due  to  this  factor.     The  centrifugal  force  applied 
for  drying  purposes  was  the  means  used  in  these  experiments  to  control 
the  method  of  packing.     The  results,  especially  during  the  last  two  periods 
of  rotation  show  that  the  system  of  packing  in  duplicate  samples  must 
have  been  closely  the  same. 

5.  Variation  in  Weight  of  Sample  Centrifuged. — The  weights  of  samples 
taken  were  purposely  varied  slightly  to  see  whether  any  change  in  the 
rate  of  drying  would  result.     The  rate  of  loss  on  drying  was  found  to  be 
fairly  constant  for  the  same  sample  and  such  variations  as  were  found 
did  not  correspond  to  the  variations  in  the  weight  of  the  sample. 

Losses  per  Gram  (see  Table  IV). — The  loss  per  gram  during  a  ten- 
minute  period  of  centrifuging  while  showing  some  variation  are  fairly 
close.  Occasional  high  and  low  results  occur  particularly  during  the  first 
two  ten-minute  periods.  It  was  considered  that  drying  conditions  would 
be  more  uniform  for  the  third  ten-minute  period  when  a  layer  of  dry  pearls 
covered  the  wet  ones  and  when  any  moisture  on  the  inside  of  the  crucibles 
and  above  the  top  layer  of  pearls  would  be  removed.  For  this  reason 
the  values  obtained  in  this  interval  were  used  in  the  calculations. 

It  is  readily  seen  that  the  loss  on  centrifuging  any  one  sample  is  pro- 
portional to  the  time  of  centrifuging,  as  would  be  expected. 

TABLE  V. 
Data  for  Centrifugal  Samples. 

Av.  Loss    Vol.  per  gm.    %  pore     Pore  space 
Sample.  Diameter.        per  gram.       (in  cc.)  space.          (in  cc.)  K. 

Ottawa  Sand 0.079  0.0084  °-59  36.26  0.22  0.136 

Pearls    7 0.054  0.0044  °-45  34-oo  0.15  0.128 

Pearls  i o 0.046  0.0057  0.60  33.40  0.20  0.136 

Pearls    8 0.041  0.0048  0.49  34.20  0.17  0.140 

A  relation  was  found  to  exist  between  the  diameter  of  the  pearls,  the 
rate  of  loss  and  the  pore  space.  Diameters  were  obtained  by  the  count- 
weight  method,  the  rate  of  loss  experimentally  by  centrifuging,  and  the 
pore  space  by  calculation  from  King's  formula.  A  tabulation  of  the 
data  is  given  in  Table  V.  The  rate  of  loss  was  found  to  vary  as  the  square 
root  of  the  diameter  and  as  the  pore  space.  Expressing  this  in  the  form 
of  an  equation  we  have 


13 

L  =  KPDH, 
in  which, 

L  =  loss  per  gram, 

P  =  pore  space,  and 

D  =  the  diameter. 

Values  of  "K"  are  shown  in  Table  V.  The  variations  in  "K"  indicate 
a  variation  of  about  0.002  cm.  in  the  diameters  obtained. 

No  application  of  this  method  was  made  to  samples  of  irregular  shapes, 
since  there  is  no  method  for  getting  a  standard  for  the  effective  diameter. 
No.  7  was  composed  of  pearls  of  two  sizes  which  accounted  in  part  for  its 
smaller  amount  of  pore  space.  The  sample  also  shows  a  low  value  for 
"K." 

While  the  results  obtained  show  the  relation  anticipated  they  do  not 
give  the  desired  degree  of  accuracy.  A  part  of  this  failure  is  no  doubt 
due  to  the  method  of  calculating  pore  space.  It  must  also  be  noted  that 
the  value  of  "K"  as  given  is  limited  to  the  crucibles  used,  since  the  loss 
per  gram  could  be  decreased  by  decreasing  the  number  of  perforations 
in  the  bottom  of  the  crucible.  Neither  pore  space  nor  diameter  would 
be  effected  by  this,  so  that  "K"  would  have  to  vary  if  the  relationship 
held. 

The  method  as  developed  gives  a  general  relationship  but  does  not  per- 
mit of  determining  the  individual  factors  in  the  equation  with  an  accuracy 
sufficient  to  warrant  its  application  in  determining  diameters  more  closely 
than  0.002  cm.  This  variation  is  too  large  for  the  diameters  considered. 
As  a  result  of  this  no  additional  work  was  done  along  this  line. 


MEASUREMENT  OF  THE  THICKNESS  OF  FILM  FORMED  ON 

GLASS  AND  SAND. 
Introduction. 

A  large  amount  of  work  has  been  done  up  to  the  present  time  on  the 
formation  of  a  film  on  the  surface  of  glass  or  silica,  in  which  water  has  been 
used  as  the  liquid  to  produce  the  film.  Thus,  Ihmori,1  Parks,2  Briggs,8 
Katz.4  and  Langmuir,6  give  values  for  the  thickness  of  the  film  formed 
on  glass,  silicate  or  quartz  surfaces. 

There  is  a  considerable  difference  in  the  values  obtained  as  might  be 
expected,  since  the  materials  used  differed  considerably  in  chemical  com- 

1  Wied.  Ann.,  31,  1006  (1887). 
*Phil.  Mag.,  [6]  5,  517  (1903). 

3  J.  Phys.  Chem.,  9,  617  (1905). 

4  Proc.  Acad.  Wetenschappen,  1915,  p.  445. 
8/.  Am.  Chem.  Soc.,  38,  2221  (1916). 


14 

position  and  nature  of  surface.  A  part  of  the  material  was  in  the  form  of 
small  grains  (sand  and  quartz),  some  being  relatively  coarse  and  some 
extremely  fine  powder.  The  glass  used  was  in  the  form  of  thin  sheets, 
in  some  cases  curved  (spherical),  and  in  others  plane.  Each  of  these 
factors  would  have  an  influence  on  the  thickness  of  film  obtained,  as  would 
also  the  temperature  and  vapor  pressure  at  which  the  film  was  formed. 
Some  typical  results  obtained  for  the  film  thickness  are  given  in  the  fol- 
lowing table : 

TABLE  I. — FILM  THICKNESS  VALUES. 

No.  Nature  of  material.  Film  thickness.  Investigator. 

1.  Glass  globes o .0000033  Ihmori 

2.  Cotton  silicate  (glass  wool) o  .0000133  Parks 

3.  Sand  (microscopic  powder) 0.00000045  Briggs 

4.  Quartz  (very  fine  powder) o  .0000013  Katz 

Anorthite  (as  above) o  .0000062  Katz 

5.  Glass  (incandescent  lamp  globes) o  .00000166  Langmuir 

There  are  two  theories  regarding  the  formation  of  a  film  on  a  solid. 
According  to  the  first  the  force  acting  is  physical  in  its  nature,  and  the 
intensity  of  its  effect  varies  inversely  as  some  power  of  the  distance  be- 
tween the  two  molecules  concerned.  The  force  is  similar  to  the  force  of 
gravitation  but  acts  through  the  distance  between  molecules.  According 
to  this  theory  successive  layers  of  molecules  may  be  built  up  on  the  surface 
of  a  solid  to  a  thickness  such  that  the  attractive  force  of  the  solid  just 
equals  the  tendency  of  the  outer  layer  of  the  film  to  evaporate. 

The  second  theory  assumes  that  a  chemical  reaction  takes  place  and 
that  the  water  taken  up  becomes  a  part  of  a  more  or  less  stable  chemical 
compound.  According  to  this  theory  a  variable  amount  of  water  could 
be  taken  up  by  solids  depending  only  on  the  capacity  of  the  solid  to  form 
a  loose  compound  with  it. 

The  second  theory  has  usually  been  assumed  to  hold  for  the  film  of 
water  forming  on  glass  surfaces,  free  or  loosely  combined  alkali  present 
in  the  glass,  being  the  substance  with  which  the  water  reacts.  Ihmori,1 
found  that  keeping  the  glass  in  boiling  water  for  some  time  decreased  the 
amount  of  water  which  it  would  take  up.  He  believed  that  alkali  was 
removed  during  this  boiling,  and  that  the  decrease  in  the  amount  of 
moisture  taken  up  was  due  to  this  fact. 

It  seemed  worth  while  to  check  the  values  obtained  using  glass  and 
sand,  having  known  surfaces,  if  possible.  Since  no  work  had  been  done  to 
determine  the  thickest  film  which  can  form  without  free  liquid  ap- 
pearing, a  method  of  doing  this  was  worked  out.  This  film  was  com- 
pared with  the  film  formed  with  other  liquids  to  see  whether  there  was  any 
basis  for  the  theory  that  a  chemical  compound  formed  with  water. 
1  Loc.  cit. 


15 

Materials. 

Solids:  Sand. — Ordinary  river  sand  was  used.  It  was  treated  with 
cone,  hydrochloric  acid  until  no  test  for  iron  was  shown.  The  acid  was 
then  washed  out  with  distilled  water  and  the  sample  dried  in  the  ah". 
Four  samples  were  obtained  by  sifting.  The  first  sample  contained  all  of 
the  sand  which  passed  the  lo-mesh  screen  but  was  retained  by  the  20- 
mesh  screen.  The  second,  third  and  fourth  samples  consisted  of  the 
fractions  from  the  original  lot  retained  by  the  40-,  60-  and  8o-mesh 
screens,  respectively.  These  are  called  10-,  20-,  40-  and  6o-mesh  sands 
in  this  paper. 

The  grains  in  this  lot  of  sand  were  far  from  spherical,  no  two  diameters 
being  the  same.  An  approximation  of  the  surface  was  obtained  by  weigh- 
ing a  counted  number  of  grains  (4000  to  5000),  to  get  the  average  weight 
per  grain,  and  determining  the  specific  gravity.  On  the  assumption  that 
the  grains  were  spherical  the  diameter  and  surface  of  a  single  grain  could 
be  calculated.  It  was  realized  when  these  values  were  obtained  that  they 
were  at  best  only  approximations. 

Ottawa  Sand. — A  single  sample  of  sand  called  in  this  paper  "Ottawa 
Sand,"  consisted  of  well-rounded  grains.  This  sample  gave  values  by  the 
above  mentioned  method  which  were  very  close  to  the  true  value  for  the 
diameter  and  surface.  It  was  considered  to  be  of  known  surface. 

Glass  Pearls. — The  glass  pearls  used  were  solid,  round  and  of  various 
sizes,  as  indicated  in  the  table  below.  A  few,  which  were  poorly  formed, 
were  removed  from  the  lot  by  rolling  them  down  an  inclined  board. 
Those  which  were  not  round  could  be  easily  picked  out  in  this  way.  The 
pearls  were  from  two  different  sources,  and  apparently  of  different  kinds 
of  glass.  They  differed  considerably  in  specific  gravity. 

The  first  lot  was  purchased  at  retail.  The  material  was  sold  under  the 
name  of  "Glistening  Dew"  and  was  used  to  decorate  fancy  cards.  Two 
samples  were  obtained  from  this  lot  by  "elutriation."  A  quantity  of  the 
pearls  were  placed  in  a  tube  and  delivered  from  it  at  a  slow  rate  into  a 
rising  column  of  water.  Under  these  conditions  by  properly  regulating 
the  current,  the  lighter  ones  were  carried  up  and  the  heavier  ones  sank 
to  the  bottom.  These  samples  are  No.  9  and  No.  10,  in  the  tables. 

The  second  lot  consisted  of  5  samples,  Nos.  i,  3,  5,  7,  and  8.  The 
individual  pearls  in  each  sample  were  of  the  same  diameter  except  for 
No.  7  which  contained  pearls  of  two  sizes.  These  samples  were  obtained 
from  Germany  and  when  received  were  coated  with  dye. 

All  of  the  samples  were  cleaned  by  boiling  in  cone,  nitric  acid,  washing 
free  from  acid  and  air  drying.  The  diameter,  surface  and  volume  of  the 
pearls  in  each  lot  were  determined  by  the  method  used  for  the  sand. 

Liquids. — Distilled  water  and  a  series  of  organic  liquids  were  used  to 
form  the  films. 


Specific  Gravity  of  Solids. — The  specific  gravity  of  the  sand  and  the 
pearl  samples  was  determined  by  displacement  of  water.  A  specific 
gravity  bottle  was  weighed,  empty,  full  of  water,  and  then  with  a  known 
weight  of  sample  substituted  for  a  part  of  the  water.  To  avoid  air  bubbles, 
the  weighed  sample  was  run  into  water  in  a  fine  stream.  The  bottle  was 
then  placed  in  a  partial  vacuum  and  let  stand  for  several  hours  before 
the  final  filling  and  weighing  was  done. 

Method  of  Determining  Film  Thickness. — In  most  of  the  previous 
work  done  on  determining  film  thickness,  the  film  has  been  formed  by 
subjecting  the  sample  to  the  vapors  of  water  and  establishing  an  equilib- 
rium at  the  contact  surface.  Usually  the  water  vapor  was  at  or  near  its 
saturation  point.  As  a  check  on  the  results  obtained  in  this  way,  the 
method  used  in  this  paper  was  evolved,  which  consists  in  getting  an 
equilibrium  of  the  film,  by  the  use  of  liquid  water  rather  than  vapor,  and 
getting  it  with  the  air  saturated.  This  would  give  the  maximum  film 
which  could  form,  and  at  the  same  time,  would,  by 
the  magnitude  of  the  results  obtained,  indicate 
whether  there  was  an  essential  difference  between  a 
film  formed  from  the  vapor  and  one  formed  from  the 
liquid. 

Considering  the  sand  and  pearl  samples  already  de- 
scribed, the  method  involves  the  addition  of  small 
amounts  of  liquid  to  them,  thus  gradually  building  up 
on  them  a  film  of  water.  As  successive  layers  of 
molecules  are  added  to  this  film  a  thickness  is  finally 
reached  at  which  the  surface  molecules  act  as  normal 
molecules.  That  is  they  evaporate,  flow,  exert  surface 
tension,  etc.  Any  liquid  beyond  this  amount  would 
remain  in  the  liquid  condition.  It  was  only  necessary 
to  get  a  definite  test  for  the  point  at  which  these  new 
properties  exhibit  themselves. 

Apparatus. — The  first  and  simplest  arrangement  used 
for  this  purpose  consisted  of  a  buret  and  an  Erlen- 
meyer  flask.  The  weighed  sample  of  sand  was  placed 
in  the  flask  and  liquid  added  from  the  buret  a  drop  at 
a  time,  with  thorough  shaking  between,  until  a  final 
drop  caused  the  grains  to  stick  to  the  flask.  When 
this  occurred  water  was  present  as  free  liquid.  This 
"sticking  point"  was  taken  as  the  end -point  of  the 
titration.  Fig.  i. 

An  ordinary  buret  soon  proved  unsatisfactory  for  delivering  the  liquid, 
especially  so  in  cases  where  the  liquid  was  volatile.  Delivering  the 


17 

liquid  into  an  open  flask  also  introduced  errors  with  these  liquids.  To 
avoid  these  losses  due  to  volatility  of  the  liquids,  and  to  limit  definitely 
the  volume  of  air  saturated  during  a  titration,  a  weight  buret,  Fig.  i, 
was  substituted  for  the  ordinary  buret  and  the  liquid  was  delivered  into 
a  closed  flask. 

Procedure. — In  carrying  out  a  single  determination  the  following 
procedure  was  used:  200  g.  of  the  air- dry  sample  was  weighed  and 
transferred  to  the  clean,  dry,  Brlenmeyer  flask.  The  flask  was  then 
closed  by  means  of  the  stopper  carrying  the  weight  buret.  The  liquid 
was  run  in  a  drop  at  a  time,  the  sand  being  thoroughly  shaken  after 
the  addition  of  each  drop.  Toward  the  end  of  the  titration  only  frac- 
tions of  a  drop  were  added,  these  being  removed  by  tipping  the  flask 
to  bring  the  pearls  in  contact  with  the  tip  of  the  buret. 

A  final  addition  of  liquid  caused  a  large  number  of  the  pearls  to.  stick 
to  the  walls  of  the  flask.  The  weight  of  the  liquid  used  gave  the  amount 
of  liquid  taken  up  when  a  film  of  maximum  thickness  formed.  Correc- 
tions were  made  in  the  case  of  volatile  liquids  for  the  amount  of  liquid 
necessary  to  saturate  the  air  in  the  flask  under  the  working  conditions. 

After  a  determination  in  which  sand  was  used  the  sand  was  air-dried 
and  then  heated  to  strong  redness  in  a  large  platinum  dish.  After  partial 
cooling  it  was  transferred  to  a  desiccator  over  phosphorus  pentoxide,  and 
kept  for  future  determinations.  The  pearl  samples  were  not  ignited. 
They  were  boiled  with  strong  nitric  acid,  to  which  some  hydrochloric 
was  added  and  were  air-dried  after  being  washed  free  from  acid. 

This  procedure  was  followed  for  the  purpose  of  determining  whether  a 
chemical  reaction  was  involved  in  the  holding  of  the  liquid.  If  the  pearls 
were  air-dried,  there  would  be  much  less  tendency  for  an  unstable  chemical 
compound  to  be  broken  down,  than  if  they  were  dried  in  vacua.  The 
intention  was  to  have  the  chemical  compound,  if  it  formed  at  all,  present 
at  the  time  of 'titration,  and  not  formed  during  it.  It  seemed  improbable 
that  any  chemical  compound  formed  by  the  method  used,  would  decom- 
pose on  exposure  to  ordinary  conditions  of  temperature  and  pressure. 

Experimental. — In  order  to  obtain  the  relationship  between  surface 
and  amount  of  liquid  to  produce  sticking,  a  series  of  determinations  was 
conducted  using  the  glass  pearls,  water  being  used  as  the  titrating  liquid. 
Under  these  conditions  the  only  variables  were  those  of  the  solid,  in- 
cluding the  nature  of  the  surface,  the  size  and  the  specific  gravity  of  the 
pearls.  For  samples  from  the  same  source  no  difference  in  the  nature 
of  the  surface  was  to  be  expected. 

During  the  whole  of  this  work  an  attempt  was  made  to  find  other 
material  suitable  for  titration  and  of  known  surface.  Results  with  this 
material  would  permit  conclusions  to  be  drawn  regarding  the  capacity 


i8 

of  different  surfaces  to  hold  liquid  films  and  would  thus  show  the  effect 
of  the  other  variants.  No  other  material  was  found  that  could  be  used 
in  this  way. 

Reproducibility  of  Results. — The  apparatus  as  used  was  subject  to 
some  error  due  to  the  fact  that  the  quantity  of  liquid  added  could  only  be 
controlled  by  opening  the  lower  stopcock  of  the  weight  buret.  To  give  an 
idea  of  the  accuracy  obtainable  with  this  apparatus,  a  series  of  results 
obtained  with  each  of  two  liquids  is  included.  The  remaining  liquids 
gave  results  correspondingly  accurate. 

Liquid.  Water.  Nitrobenzene. 

Sample 200  g.  pearls  No.  8  200  g.  pearls  No.  3 

Weight  of  liquid,  grams o .  1 19  o  .040 

0.119  o  041 

0.117  0.039 

o.i 16  0.042 

O.I2O  O.042 

O.I2I  0.038 

O  Il6 

0.118 

Average 0.118  o  .040 

Greatest  variation  from  average o  .003  =2.5%  =  5  % 

Variation  between  highest  and  lowest  values          4.2%  10% 

The  per  cent,  error  introduced  depended  principally  on  the  amount  of  surface  titrated 
or  on  the  amount  of  liquid  added,  the  greatest  variation  amounting  to  from  0.004 
to  0.006  g.  of  liquid. 

The  results  obtained  and  the  calculations  of  film  thickness  are  given 
in  the  accompanying  table: 

TABLE  II. — TITRATION  VALUES  USING  WATER. 


Sample. 

Diameter 

Surface 

Titration 

Film 

Pearls. 

in  cm. 

sq.  cm./g. 

Sp.  gr. 

Weight. 

liquid  per  g. 

thickness. 

No   i 

O    I  "^67 

14   6? 

•7       IOI 

o  .003988 

o  .  ooo  1  90 

o  .00001  29 

No.  3.. 

\j  .  *  3*j  / 
O  .  1  1  80 

**f  •  ^  / 
17  .09 

O  •  *  ^Jx 
1    OQO 

o  .002626 

O   OOO2  I  8 

o  .0000128 

No.  5  

0.0808 

24.03 

O  •  **ar^* 

3.079 

o  000853 

0.000303 

0.0000126 

No.  7  , 

o  .0542 

35  -46 

3  •  I25 

o  .000261 

o  .  000402 

o  .00001  13 

No.  8  

0.0410 

46.40 

3-069 

O.OOOI2I 

0.000595 

0.0000128 

No  o 

o  .0540 

44    Q-J 

2    SOS 

o  .000206 

O   OOO207 

o  .  0000066 

No.  10  

0.0460 

*1^T  •  7O 

53  •  *4 

^  •  owo 

2  .496 

O  .  OOO  122 

\j  .  wt_rv^^*y  i 

o  .000375 

o  .0000070 

SANDS. 

^y 

Ottawa  

0.0790 

28.58 

2.656 

0.000686 

0.000374 

o  0000130 

lo-mesh  

o  .  0494 

46.00 

2.643 

0.000168 

O.OOI3IO 

0.0000285 

2O-mesh  

0.0430 

52.28 

2.646 

O.OOOI  IO 

O.OOI  I2O 

0.0000214 

4O-mesh  

0.0280 

81  .90 

2.650 

0.000030 

O.OOI  IOO 

0.0000135 

6o-mesh  

0.0170 

129  57 

2.666 

0.000007 

0.001480 

0.0000114 

Discussion  of  Results. — The  liquid  required  for  a  titration  may  be 
used  to  form  a  uniform  film  of  liquid  over  the  surface  of  the  pearls  up  to 


19 

the  thickness  at  which  flow  would  occur.  If  this  is  the  case  a  negligible 
amount  of  liquid  would  be  required  actually  to  support  the  grains,  this 
amount  being  added  after  the  uniform  film  had  been  added,  and  "stick- 
ing" would  result  from  a  concentration  of  this  added  amount  at  the  con- 
tact surface  of  flask  and  pearl  through  the  action  of  capillary  forces. 

On  the  other  hand,  the  whole  amount  of  liquid  required  may  be  neces- 
sary to  support  the  pearls  through  the  action  of  surface  tension.  In  this 
case  no  film  would  form  but  all  of  the  liquid  added  would  concentrate 
at  the  contact  surface,  and  "sticking"  would  occur  as  soon  as  the  surface 
tension  was  sufficient  to  support  the  pearl. 

In  order  to  determine  which  of  these  two  hypotheses  held  or  whether 
the  amount  used  in  titrating  was  the  resultant  of  both  effects,  some 
calculations  were  made  of  the  amount  of  liquid  necessary  to  support  a 
single  grain.  Fig.  2  will  explain  the  letters  used  and  the  method  of 
calculation  followed. 

Consider  a  pearl  weighing  o.oooi  g.,  held  to  the  surface  of  the  flask  by 
surface  tension.  The  liquid  holding  the  pearl  may  be  considered  as 
occupying  a  volume  represented  in  section  by  (OBCED),  the  lowest 
level  of  this  volume  being  the  circumference  of  a  circle  whose  radius  is  a. 
Surface  tension  may  be  considered  as  acting  along  this  circumference.  If  the 
surface  tension  and  the  weight  supported  by  it  are  known,  the  length  of 


Fig.  2. 

the  circumference  required  to  support  the  pearl  is  given  o.oooi /sur.  ten. 
Substituting  actual  values  and  placing  the  quotient  equal  to  the  circum- 
ference of  a  circle  enables  one  to  calculate  the  value  of  a  in  the  same 
units  as  are  used  for  expressing  the  surface  tension  (cm.).  Having  the 
value  of  a,  the  value  of  h  (thickness  of  liquid  acting)  may  be  calculated, 
since  by  geometry, 


2O 


and  all  of  the  terms  except  h  are  known. 

Knowing  both  a  and  h,  the  volume  of  liquid  holding  the  pearl  can  be 
estimated.  It  was  assumed  that  the  volume  of  liquid  necessary  to  sup- 
port the  pearl  would  be  that  required  to  half  fill  the  volume  represented 
on  the  figure  by  (OB ED).  This  is  believed  to  be  in  excess  of  the  actual 
amount  needed.  Calculating  this  value  for  the  smallest  pearl  used,  one 
weighing  0.00012  g.  gave  0.0537  cc-  P61"  g-  °f  pearls.  Calculating  the  same 
value  for  pearls  No.  i,  the  heaviest  pearls  used,  gave  0.058  cc.  per  g.  of 
pearls.  These  amounts  are  negligible  when  the  amounts  required  for  a 
titration  are  considered.  This  shows  clearly  that  although  the  end- 
point  is  marked  by  the  appearance  of  "sticking,"  which  is  a  surface-tension 
effect,  surface  tension  itself  cannot  account  for  the  liquid  required  for  a 
titration. 

The  amount  of  liquid  required  is  directly  proportional  to  the  surface, 
and  the  film  thickness  is  uniform  for  the  same  kind  of  glass. 

As  to  the  actual  thickness  of  film  found,  it  is  of  the  same  order  as  that 
found  by  earlier  investigators  who  worked  with  the  vapor  phase  of  water 
in  forming  the  film.  The  results  are  higher  than  those  of  all  except 
Parks.  It  does  not  seem  probable,  in  view  of  the  results  obtained,  that 
there  is  any  difference  in  the  nature  of  the  film  itself,  whether  water  in  the 
vapor  phase  or  water  in  the  liquid  phase  is  used  to  form  the  film.  It  also 
seems  probable  that  what  actually  takes  place  on  the  surface  of  the  grain 
is  a  condensation  of  water  vapor.  In  the  titrations  in  which  water  was 
used  to  form  the  film  it  was  found  that  the  titrated  sample  on  air  drying, 
wou1d  again  take  up  the  same  amount  of  liquid.  It  is  difficult  to  see 
how  this  could  take  place  repeatedly  if  a  chemical  reaction  was  involved 
in  holding  the  liquid. 

The  results  obtained  with  samples  No.  9  and  No.  10,  are  only  about 
half  as  large  as  those  obtained  with  the  rest  of  the  samples.  This  can 
only  be  due  to  a  different  surface  capacity  for  holding  liquid.  The  results 
are  close  to  those  obtained  by  Katz  with  ornithite,  and  by  Ihmori  with 
glass  globes. 

Ottawa  sand  gives  the  same  value  for  film  thickness  that  the  larger 
series  of  pearls  does.  It  seems  probable  that  this  is  a  chance  agreement, 
since  the  surface  of  the  sand  differed  considerably  from  that  of  the  pearls, 
both  in  hardness  and  in  texture. 

As  a  whole  the  results  indicate  that  there  are  two  factors  which  in- 
fluence the  amount  of  liquid  necessary  to  form  the  maximum  thickness 
of  film.  The  first  factor  is  the  amount  of  surface,  the  actual  area  that  the 
film  must  cover.  The  second  is  the  nature  of  the  surface  itself,  its 
capacity  to  hold  a  film. 


21 

Not  a  great  deal  is  known  regarding  the  variants  which  determine  the 
capacity  factor  of  a  surface.  It  is  probably  related  to  the  free  energy 
present  in  the  atoms  of  the  surface  layers. 

The  work  up  to  this  point  indicated  that  the  film  thickness  should  be 
independent  of  the  liquid  used,  providing  the  liquid  is  not  too  viscous 
to  spread  readily.  It  also  indicated  the  desirability  of  applying  the 
titration  method  to  the  determination  of  the  surface  of  irregular  particles 
like  sand  grains. 

For  the  purpose  of  obtaining  surface  values  for  the  meshed  sands, 
complete  titrations  for  each  of  these  samples  with  water  and  with  each 
of  the  organic  liquids  was  carried  out.  An  attempt  was  made  also  to 
titrate  finer  sands,  loo-mesh,  i5o-mesh,  2oo-mesh.  These  however, 
would  not  permit  of  an  even  distribution  of  the  liquid  over  the  surface, 
and  no  satisfactory  titrations  were  obtainable. 

To  determine  whether  the  same  thickness  of  film  would  be  found  with  a 
different  liquid,  titrations  were  carried  out  first  with  the  pearls  and  then 
with  the  sands  making  use  of  the  organic  liquids.  The  determinations 
with  the  pearls  were  not  completed  when  they  were  found  to  check  closely 
for  the  first  liquids  used  but  those  on  the  sands  were  completed  for  all 
of  the  liquids. 

The  organic  liquids  used  were  chosen  so  that  the  specific  gravity, 
volatility,  surface  tension,  etc.,  varied. 

The  results  obtained  from  these  two  series  of  titrations  are  given  in 
Table  III,  and  will  be  discussed  together. 

TABLE  III. — TITRATION  VALUES  FOR  SANDS  AND  PEARLS  WITH  ORGANIC  LIQUIDS. 


Liquids. 

Nitrobenzene 

K 
o 

Sands. 

)-mesh.            20-mesh. 
.00136          O.OOII7 
.00133           O.OOIO8 
00122            0.00107 
.00131            0.00108 
.OOI26           O.OOII2 
.00134           O.OOII6 
.00131            O.OOII6 

40-mesh. 
0.00109 
O.OOII2 
O.OOIO9 
0.00107 
O.OOII2 
O.OOIIO 
O.OOIOS 
O.OOIO9 

No.  8. 
0.00056 
0.00059 
0.00055 
0.00059 
0.00059 
0.00053 

60-mesh. 
0.00148 
O.OOI5I 
0.00148 
0.00155 
0.00149 
0.00146 
0.00142 

No.  9. 
0.00027 
0.00030 
O.OOO23 
0.00029 
0.00030 
0.00031 

Ottawa. 
0.00039 
0.00037 
0.00039 
0.00039 
0.00039 
0.00038 
0.00039 

No.  10. 
0.00040 
0.00037 
0.00039 
0.00045 
0.00039 
0.00038 

Water  

o 

Aniline      

o 

Dimethylaniline 

o 

Phenyliodide  

o 

Toluol     

o 

Turpentine 

o 

Pyridine  

Liquids. 

N  i  trobenzene 

No.  1. 
0.00018 
0.00019 

Pearls. 
No.  3.             No.  5. 
0.00020         0.00030 
O.OOO22         O.OOO3O 

0.00022          0.00032 
0.00021 

Water  

Aniline  

Dimethylaniline  .  .  . 
Phenyliodide  
Toluol.  . 

0.00017 
0.00018 

22 

Discussion  of  Results. — The  results  show  that  the  thickness  of  the 
film  is  independent  of  the  kind  of  liquid  used  for  titrating,  and  that  the 
sand  titrations  can  be  checked  with  as  good  an  accuracy  as  titrations  of 
pearls.  Occasional  results  vary,  but  the  uniformity  for  the  whole  series 
is  pronounced.  This  proves  definitely  that  the  surface  tension  of  the  liquid 
has  no  effect  on  the  amount  of  liquid  required  for  a  titration.  The  surface 
tension  of  water  is  much  greater  than  that  of  the  other  liquids  but  the 
volume  required  per  gram  is  the  same.  This  could  not  be  true  if  the 
surface  tension  influenced  the  amount  of  liquid  required  to  produce 
"sticking." 

It  also  proves  that  there  is  no  chemical  reaction  in  the  ordinary  sense 
•of  the  term,  when  a  film  of  water  forms  on  glass.  While  it  might  be 
possible  to  imagine  such  an  effect  between  water  and  glass,  it  is  obviously 
impossible  to  do  so  with  the  rest  of  the  liquids  of  the  series.  In  addition 
to  this  the  calculated  film  thickness  for  different  sizes  of  pearls  is  found 
to  be  the  same,  showing  that  the  volume  for  titration  varies  with  the 
surface. 

The  definite  conclusion  can  be  drawn  that  these  films  are  not  due  to 
the  formation  of  a  chemical  compound,  but  that  they  are  held  by  the  free 
surface  energy  of  the  solid.  It  seems  certain  that  the  same  force  holds  a 
thinner  film. 

While  these  films  are  formed  by  the  addition  of  liquid  to  the  solid,  the 
inference  is  that  the  same  conclusion  may  be  drawn  for  a  film  formed 
from  the  vapor  phase.  This  inference  is  supported  by  the  fact  that  the 
values  obtained  for  the  film  thickness  when  formed  from  the  vapor  phase 
are  only  very  slightly  lower  than  those  formed  by  the  addition  of  liquid. 
It  seems  probable  that  a  liquid  film  forms  in  both  cases,  but  that  with  the 
unsaturated  vapor  phase  it  never  becomes  thick  enough  to  show  as  a 
normal  liquid  on  the  surface  of  the  solid,  while  when  liquid  is  used  the 
formation  of  free  liquid  marks  the  end  of  the  titration  and  indicates  the 
thickest  film  that  can  form  without  free  liquid  being  present. 

In  titrating  sands  a  simple  relationship  such  as  was  found  for  the  pearl 
samples  does  not  exist  between  titrated  amount  and  calculated  surface. 
This  is  partly  due  to  error  in  calculating  the  surface,  on  the  assumption 
that  the  grains  are  spherical,  and  partly  to  the  fact  that  extra  liquid  is 
required  to  fill  the  etchings  in  the  surface.  However,  if  relative  effective 
surfaces  are  sought  they  may  be  expected  to  be  proportional  to  the  titra- 
tion values  since  there  is  no  application  of  the  surface  which  would  not 
involve  the  etchings  and  so  produce  results  which  would  be  proportional 
to  those  obtained  by  the  titration  method. 


23 

Summary. 

This  paper  describes  a  new  method  of  obtaining  the  thickness  of  the 
maximum  film  which  can  form  on  a  surface  without  free  liquid  being 
present.  Evidence  is  presented  to  show  that  the  liquid  forming  the  film 
does  not  combine  chemically  with  the  solid.  The  method  has  been  applied 
to  sand  and  to  glass,  and  films  have  been  formed  with  water  and  with 
several  organic  liquids.  The  film  thickness  is  found  to  be  independent 
of  the  liquid  used  and  of  the  size  of  the  solid  particle.  The  method  gives 
accurate  values  for  the  effective  surface  of  sand  particles,  providing  that 
surfaces  of  the  same  kind  are  compared. 


PART  II.— THE  ADSORPTION  OF  COPPER  SULPHATE  BY  GLASS 

AND  SAND. 

Introduction. — Adsorption  has  been  applied  as  a  general  term  to  in- 
clude any  one  or  a  group  of  effects  taking  place  at  the  contact  surface 
between  two  different  phases.  In  a  specific  case  it  may  be  a  capillary 
effect,  or  an  adsorption,  or  a  chemical  change.  Or  it  may  be  a  combina- 
tion of  two  or  more  of  these.  The  term  "Adsorption"  as  at  present  used, 
indicates  simply  that  the  action  taking  place,  which  is  always  a  change  in 
concentration,  is  limited  roughly  to  the  surface,  and  is  relatively  small  in 
amount. 

In  view  of  the  fact  that  the  term  is  used  to  include  so  many  effects  that 
may  differ  entirely  in  their  nature,  such  as  the  formation  of  a  film  of  liquid 
or  gas  on  any  solid,  the  accumulation  of  any  dissolved  substance  on  the 
surface  of  any  solid,  liquid,  or  gas  in  contact  with  its  solution,  etc.,  it  is 
not  surprising  that  the  equation  used  to  express  the  relation  between  ad- 
sorption and  the  factors  which  influence  it,  must  be  a  general  one.  On 
the  contrary,  it  is  surprising  that  any  equation,  no  matter  how  general, 
will  apply  to  so  many  seemingly  different  processes. 

The  equation  which  is  generally  used1  for  the  adsorption  isotherm,  and 
which  has  been  found  to  hold  for  a  good  many  individual  cases,  is  as  follows : 

X/M  =  kCn. 
in  which, 

X  is  the  amount  adsorbed, 

M  is  the  mass  of  the  adsorbing  substance, 

C  is  the  concentration  of  the  adsorbed  substance, 

"k"  and  '  V  are  constants  depending  on  the  materials  used. 

"n"  may  be  positive  or  negative,  whole  or  fractional. 
1  Zeit.  Phys,  Chemie,  57-425,  1906. 


24 

It  will  be  noted  that  the  equation  as  given  does  not  include  the  surface 
factor  at  all,  in  spite  of  the  fact  that  adsorption  is  defined  as  a  "change 
in  concentration  of  the  adsorbed  substance  at  the  surface  of  contact." 
Its  omission  is  brought  about  chiefly  by  two  factors,  the  necessity  of  using 
very  large  surfaces  in  order  to  get  a  measurable  effect,  and  the  practical 
difficulties  involved  in  the  subjection  of  a  large,  known  surface  to  adsorp- 
tion. 

The  solid  materials  ordinarily  used  for  an  adsorbing  surface  are  in  a 
finely  divided  condition  in  order  to  increase  the  surface  as  much  as  possible, 
without  at  the  same  time  increasing  the  bulk  of  the  material  used.  With 
material  of  this  kind  it  is  very  probable  that  the  relation  between  surface 
and  weight  is  contant.  That  is,  two  grams  of  finely  ground  charcoal, 
clay,  or  silica,  have  a  surface  double  that  of  one  gram  of  the  same  sample 
of  material.  In  order  for  this  to  hold  exactly,  it  is  necessary  to  assume 
that  the  particles  of  the  portions  of  the  adsorbing  substance  used  are  all 
of  the  same  mean  size,  but  even  without  this  assumption,  the  results  ob- 
tained by  substituting  mass  for  surface  would  be  more  accurate  than 
those  based  on  the  values  of  the  surface  derived  in  any  other  way  known 
at  the  present  time.  In  effect  then,  the  term  "M,"  in  the  equation  given 
above  is  a  relative  measure  of  the  surface  involved. 

If  we  view  adsorption  as  a  purely  physical  effect,  a  change  in  concen- 
tration without  chemical  reaction  occurring,  and  produce  it  upon  a  known 
surface,  and  with  a  known  concentration  of  a  solute,  the  adsorption  per 
unit  surface  should  be  a  constant  quantity.  Since  the  same  materials 
are  used,  "k"  and  "n"  should  have  constant  values,  and  if  "C"  is  also  kept 
constant,  X/M  or  X/S  should  give  a  constant  value  (S,  represents  the 
surface). 

Much  attention  has  been  given  to  the  solubility  of  glass  in  acid,  alkali, 
and  salt  solutions,  in  order  to  determine  to  what  extent  the  error  introduced 
from  this  source,  influences  analytical  results. 

No  attempt  has  been  made,  so  far  as  our  study  of  the  literature  reveals, 
to  determine  whether  glass  has  a  tendency  to  concentrate  certain  metallic 
ions  or  compounds  on  its  surface,  either  by  a  process  of  physical  adsorp- 
tion, or  by  a  double  decomposition,  resulting  in  a  solution  of  the  glass  and 
the  precipitation  of  the  metal  on  the  surface  It  is  obvious,  however, 
that  if  a  concentration  of  the  solute  or  of  one  of  its  ions  does  take  place 
on  the  surface  of  the  glass,  it  only  takes  place  to  a  very  slight  extent, 
since  the  exactness  of  quantitative  procedure  would  reveal  even  small 
variations  from  this  cause. 

Purpose  of  the  Work. — Since  glass  is  so  universally  used  in  analytical 
work  as  a  container  for  sojutions  of  all  kinds,  it  seemed  worth  while  to 
attempt  to  measure  the  increase  in  concentration  at  the  surface  of  glass, 


25 

in  a  specific  case.  The  determination  of  the  increase  in  concentration, 
or  the  adsorption,  with  a  given  solution,  and  the  variation  in  amount 
adsorbed  with  the  concentration  of  the  solution,  were  both  of  importance. 

If  increase  in  concentration  took  place,  it  might  result  from  causes 
which  were  purely  physical,  and  it  might  result  from  a  chemical  reaction 
occurring  at  the  contact  surface.  With  pure  silica  a  chemical  reaction 
would  not  be  expected.  Comparative  values  using  silica  might  help  to 
decide  whether,  when  glass  is  used,  the  adsorption  is  physical  or  chemical 
It  was  hoped  that  a  critical  examination  of  all  of  the  results  obtained  would 
lead  to  a  definite  conclusion  concerning  the  nature  of  the  process. 

In  all  of  the  work  on  adsorption  that  has  been  done  up  to  the  present  time, 
only  one  size  of  particle  has  been  used,  and  the  total  surface  exposed  has 
been  varied  by  increasing  or  decreasing  the  weight  of  this  sample.  The 
pearl  samples  described  in  the  former  paper  afforded  an  adsorbing  medium 
of  known  surface.  The  surface  of  the  meshed  sand  samples  was  also  known 
approximately.  Both  materials  had  shown  the  surface  relationship  when 
water  was  adsorbed.  If  the  adsorption  was  purely  physical,  results  similar 
to  those  obtained  with  water,  in  the  former  paper  could  be  expected.  The 
use  of  these  samples  also  permitted  us  to  vary  the  surface  exposed  without 
varying  the  weight  of  sample  exposed.  If  the  adsorption  depended  pri- 
marily on  the  surface  exposed,  its  amount  would  vary  as  the  surface  varied. 
If  other  factors  were  involved,  such  as  the  mass  of  the  individual  particles, 
this  surface  relationship  would  not  be  found.  The  only  objection  to  this 
material  was  that  the  size  of  the  grains  necessarily  limited  the  surface 
which  could  be  exposed  for  adsorption,  which  would  result  in  very  small 
adsorption  values. 

Copper  sulfate  was  chosen  as  the  substance  to  be  adsorbed,  principally 
because  of  the  ease  and  accuracy  with  which  the  copper  present  could  be 
determined.  No  precipitation  or  filtration  was  required,  a  point  of  very 
great  importance  when  very  dilute  solutions  are  used.  The  adsorption 
of  copper  sulfate  by  glass  might  be  either  physical  or  chemical  in  its  nature. 
Since  we  desired  to  study  an  adsorption  which  might  result  from  either 
in  order  to  distinguish  between  them,  it  fulfilled  the  requirements  in  this 
regard  also. 

Materials. — Pearl  samples  and  meshed  sands,  as  in  the  previous  paper. 

Copper  sulfate  solutions  made  up  from  carefully  recrystallized  copper 
sulfate. 

Method. — The  method  used  consisted  in  placing  one  hundred  grams 
of  the  pearls  in  a  clean  dry  Erlenmeyer  flask.  Over  this  was  poured  one 
hundred  cc.  of  the  copper  solution.  After  shaking  and  letting  stand  for 
a  definite  time,  ten  cc.  of  the  liquid  was  pipetted  off  and  the  copper  present 
in  it  determined  volumetrically.  This  was  repeated  at  the  intervals  noted 
in  the  tables. 


26 

In  order  to  be  sure  of  the  end  point  used,  and  also  to  check  any  varia- 
tion in  value  of  the  titrating  solution,  a  blank  was  run  before  and  after 
each  series  of  determinations.  The  blank  consisted  in  the  titration  of  a 
ten  cc.  portion  of  the  solution  being  used,  with  no  pearls  present.  A 
lower  titration  value  for  the  solution  taken  from  the  pearls,  than  that  ob- 
tained by  running  a  blank,  indicated  that  an  adsorption  had  taken  place. 

The  iodide  titration  method  was  used  to  determine  the  amount  of  copper 
present  in  the  solution.  Ammonia  was  added  to  a  portion  which  had  been 
pipetted  off,  until  an  excess  was  present,  as  indicated  by  the  appearance 
of  a  deep  blue  color.  Acetic  acid  was  next  added  to  acid  reaction,  fol- 
lowed by  about  a  gram  of  potassium  iodide.  The  iodine  liberated  was 
titrated  with  sodium  thiosulfate  solution,  and  the  copper  present  calculated 
from  the  amount  of  thiosulfate  required. 

In  titrating  these  dilute  solutions  it  was  found  that,  after  the  disap- 
pearance of  the  blue  color,  a  light  reddish  violet  color  persisted,  a  few  ad- 
ditional drops  being  required  to  cause  its  disappearance.  The  titration 
was  continued  to  the  disappearance  of  the  reddish  violet  color,  as  a  more 
definite  color  change  occurred  at  that  time.  Checks  run  using  the  two  end- 
points  indicated  that  either  could  be  used  without  materially  effecting 
the  results  obtained.  The  thiosulfate  solution  used  in  titrating  was 
standardized  by  means  of  a  copper  sulfate  solution,  prepared  from  pure 
copper  foil,  and  diluted  to  a  strength  corresponding  to  that  of  the  thiosul- 
fate solution. 

Jena  glass  flasks  were  used  to  hold  the  pearls  during  adsorption  and  were 
also  used  for  the  titrations.  Any  variations  due  to  the  use  of  glass  flasks 
should  be  present  to  the  same  extent  in  the  blank  determinations. 

Experimental. — A  few  preliminary  experiments  indicated  that  it  was 
necessary  to  use  the  greatest  care  in  cleaning  and  handling  the  pearls.  If 
the  adsorption  was  physical  and  reversible,  placing  the  pearls  in  a  current 
of  running  water  for  some  time  should  remove  the  adsorbed  material. 
On  trying  this  out  with  precipitated  silica  and  with  the  pearl  samples,  it 
was  found  that  all  of  these  samples  retained  copper.  Iron  was  also  present 
in  all.  Boiling  with  aqua  regia  and  then  washing  with  distilled  water, 
and  drying,  removed  both  to  of  these  metals.  In  addition  adsorption 
values  were  greatly  reduced  after  boiling  with  aqua  regia,  showing  that  a 
great  part  of  the  effect  obtained  with  the  material  as  first  used,  was  chem- 
ical in  its  nature. 

As  a  result,  samples  subjected  to  adsorption  were  boiled  in  aqua  regia, 
washed,  and  air-dried  before  being  used  with  a  second  solution.  Check 
determinations,  using  the  same  concentration  of  copper  sulfate  solution 
as  had  been  used  previous  to  this  treatment  showed  that  this  method  of 
cleaning  the  pearls  had  no  appreciable  effect  either  on  the  individual  ad- 
sorption values  obtained,  or  on  the  shape  of  the  adsorption  curve. 


27 

The  results  obtained  are  shown  in  the  following  tables  (I  and  II).  On 
the  accompanying  plates,  curves  are  plotted  based  on  these  results.  Most 
of  the  values  represent  an  average  of  two  separate  determinations,  though 
some  of  the  later  ones  have  not  been  so  checked. 

TABUS  I. 

Adsorption  Results. 

i.  Copper  sulfate  solution  contains  0.000042  gram  Cu  per  cc. 
Values  in  terms  of  grams  Cu  adsorbed  from  10  cc.  by  100  grams  of  solid. 

•  Amount  adsorbed  in 


Samples. 

20  min. 

4H  hrs. 

29  hrs. 

51  hrs. 

Pearls  i  

O.OOOII 

0.00052 

o  .  00062 

Pearls  3  

0.00010 

o  .  00034 

0.00052 

o  .  00065 

Pearls  5  

O.OOO26 

o  .  00035 

0.00043 

O.OOO59 

Pearls  7  

0.00033 

o  .  00095 

0.00155 

0.00153 

Pearls  8  

0.00071 

o  .  00073 

0.00138 

O.OOI5I 

Sand  4o-mesh  

O.OOO25 

0.00019 

O.OOO47 

o  .  00005 

Sand  6o-mesh  

0.00004 

O.OOOI6 

0.00012 

Sand  8o-mesh  

0.00001 

0.00005 

0.00004 

Sand  Ottawa  

O.OOOO5 

0.00019 

o  .  00032 

o  .  00030 

Prec.  Silica  

O.OOII4 

0.00191 

O.OOI9I 

0.00210 

2.  Copper 

sulfate  solution 

contains  0.000113 

gram  Cu  per 

CC. 

Pearls  i  

0.00028 

0.00061 

O.OOIOO 

O.OOII5 

Pearls  3  

0.00083 

0.00104 

0.00125 

O.OOI3I 

Pearls  5  

o  .  00073 

0.00072 

0.00070 

0.00069 

Pearls  7  

0.00143 

0.00226 

0.00274 

o  .  00326 

Pearls  8  

O.OOI22 

0.00176 

0.00214 

O.OO222 

Sand  40-mesh  

0.00028 

o  .  00034 

0.00031 

0.00055 

Sand  6o-mesh  

o  .  00024 

0.00032 

0.00023 

Sand  8o-mesh  

o  .  00007 

0.00015 

O.OOOIO 

O.OOOI7 

Sand  Ottawa  

o  .  00004 

O.OOO2O 

O.OOO22 

Prec.  Silica  

0.00311 

0.00512 

0.00514 

0.00482 

3.  Copper 

sulfate  solution 

contains  0.000153 

gram  Cu  per 

CC. 

Pearls  i  

O.OOIIO 

O.OOI2O 

Pearls  3  

.  .  . 

0.00150 

O.OO2OO 

Pearls  5  

.  .  . 

o  .  00080 

O.OOIOO 

Pearls  7  

.  .  . 

0.00290 

o  .  00300 

Pearls  8  

.  .  . 

0.00240 

o  .  00300 

Pearls  9  

.  .  . 

0.00040 

o  .  00070 

Pearls  10  

o  .  00080 

o  .  00090 

4.  Copper  sulfate  solution 

contains  0.000352 

gram  Cu  per 

cc. 

Pearls  i  

O.OOOIO 

o  .  00030 

O.OOI2O 

0.00140 

Pearls  3  

0  .  00020 

o  .  00030 

0.00270 

o  .  00300 

Pearls  5  

0.00050 

0.00090 

0.00140 

0.00160 

Pearls  7  

O.OOOIO 

O.OOO2O 

0.00370 

o  .  00400 

Pearls  8  

O.OOO2O 

0.00080 

o  .  00300 

o  .  00330 

Pearls  9  

o  .  00070 

.  .  . 

0.00070 

O.OOIOO 

Pearls  10.. 

.  .  . 

28 


TABLE  I  (Continued}. 

5.  Copper  sulfate  solution  contains  0.000655  gram  Cu  per  cc. 
Values  in  terms  of  grams  Cu  adsorbed  from  100  cc.  by  100  grams  of  solid. 

Amount  adsorbed  in 


Samples. 
Pearls  i  .  .  . 
Pearls  3 

10  min. 
0.00070 
O   OO2IO 

30  min.              2^  hrs.              24  hrs. 
O.OOO8O           O.OOIOO           O.OOI2O 
0.00260           0.00290           0.00370 
0.00025            0.00040           0.00180 
O.OOI3O           O.OO3OO           O.OO4IO 
O.OO25O           O.OO28O           O.OO29O' 

0.00030         0.00040         0.00100 

O.OOI7O           O.OO28O           O.OO3IO 

ution  contains  0.00150  gram  Cu  per 
30  min.              3J£  hrs.               24  hrs. 
0.00025           0.00028           0.00031 
O.OOOlS           O.OOO25           O.OOO32 
0.00025           0.00032           0.00036 
0.00032           0.00055           0.00057 
0.00032           0.00032           O.OOO53 
O.OOO27           0.00040          0.00047 
0.00031             0.00032            0.0004.2 

49  hrs. 
0.00140 

o  .  00470 

O.OO2IO 

o  .  00470 
o  .  00300 

O.OOI4O 
O.OO29O 
CC. 
49  hrs. 
0.00032 
0.00032 
O.OOO32 
0.00083 
0.00061 

o  .  00047 
o  .  oood.8 

Pearls  5  ... 

o  00030 

Pearls  7 

.  .    .  .       o  00070 

Pearls  8  ... 
Pearls  9  ... 
Pearls  10.  . 

o  .  00070 

O  .  OOO2O 

o  00040 

6. 

Samples. 

Pearls  i  .  .  . 

Copper  sulfate  sol 

13  min. 
O.OOO29 

Pearls  3  ... 

o  00018 

Pearls  5 

O   OOOI  I 

Pearls  7  ... 

0.00018 

Pearls  8  ... 

o  00025 

Pearls  9  ... 
Pearls  10.  . 

0.00016 
.  .0.00021 

TABLE  II. 
Adsorption  Values  for  All  Concentrations  of  Copper  Sulfate  Used. 

Amount  adsorbed  from  concentration  of 


0.00150 

0  000655 

0.000352 

0.000153 

0.000113 

0.000042 

Samples. 

gm./cc. 

gm./cc. 

gm./cc. 

gm./cc. 

gm./cc. 

gm./cc. 

29  hrs. 

Pearls  i  

.  .  .  .   o  .  0003 

O.OOI2 

O.OOI2 

O.OOII 

O.OOIO 

0.0005 

Pearls  3  

,  .  ,  .    0.0003 

0.0037 

0.0027 

0.0015 

O.OOI2 

0.0005 

Pearls  5  

.  .  .  .    O.OOO4 

O.OOlS 

0.0014 

O.OOO8 

o  .  0007 

0.0004 

Pearls  7  

o  .  0006 

O.OO4I 

0.0037 

0.0029 

0.0027 

0.0015 

Pearls  8  

0.0005 

0.0029 

0.0030 

O.OO24 

O  .  OO2  I 

0.0014 

Pearls  9  

.  .  .  .  o  .  0005 

O.OOIO 

0.0007 

O.OOO4 

.... 

Pearls  10  

O.OOO4 

0.0031 

0.0008 

.... 

50  hrs. 

Pearls  i  , 

...   o  .  0003 

0.0014 

0.0014 

O.OOI2 

O.OOII 

0.0006 

Pearls  3  

...   o  .  0003 

o  .  0047 

0.0030 

0  .  0020 

0.0013 

o  .  0006 

Pearls  5  

...   o  .  0003 

O  .  OO2  I 

0.0016 

O.OOIO 

0.0007 

O.OOO6 

Pearls  7  

...   0.0008 

o  .  0047 

o  .  0040 

o  .  0030 

0.0015 

Pearls  8  

...   o  .  0006 

o  .  0030 

0.0033 

o  .  0030 

0.0022 

0.0015 

Pearls  9  

—  0.0005 

0.0014 

O.OOIO 

O.OOO7 

Pearls  10  

...  o  .  0005 

0.0029 

O.OOO9 

30  min. 

Pearls  i  

.  .  .    0.0002 

0.0008 

0.0003 

.... 

0.0003 

0.0001 

Pearls  3  

.  ,  .    O.OOO2 

o  .  0026 

o  .  0003 

O.OOO8 

O.OOOI 

Pearls  5  

.  .    O.OOO2 

O  .  OOO2 

0.0009 

O.OOO7 

o  .  0003 

Pearls  7  

.  .  .   o  .  0003 

0.0013 

0.0002 

.... 

0.0014 

0.0003 

Pearls  8  

.  .  .    0.0003 

0.0025 

0.0008 

.... 

0.0012 

0.0007 

Pearls  9  

.  .  .   o  .  0003 

0.0003 

.... 

Pearls  10  

o  .  0003 

O.OOI7 

29 

Discussion  of  Results. — The  results  in  the  above  tables  show  that  a  defi- 
nite and  positive  concentration  of  copper  takes  place  at  the  surface  of  the 
glass  pearls.  The  adsorption  is  not  large  for  any  of  the  samples  used, 
the  maximum  value  being  0.00514  gram  of  copper  adsorbed  by  30  grams 
of  precipitated  silica.  For  glass,  the  maximum  is  0.00470  gram  of  copper, 
adsorbed  by  100  grams  of  pearls.  One  hundred  grams  of  pearls  represents 
1500  sq.  cms.  to  5300  sq.  cms.  of  surface  depending  on  the  sample  used. 

Results  using  the  meshed  sand  samples  are  included  for  some  of  the 
first  concentrations  used.  The  adsorption  values  are  small  and  they  are 
very  irregular.  Since  the  surface  was  not  definitely  known,  and  since 
the  results  obtained  were  too  small  and  too  irregular  to  permit  definite 
conclusions  to  be  drawn,  these  samples  were  omitted  in  the  later  work. 

The  original  values  obtained  with  precipitated  silica  were  very  large. 
Careful  washing  and  drying  reduced  the  values  obtained  to  one-third  of 
the  former  value.  Only  thirty  grams  of  silica  could  be  used  with  200  cc. 
of  copper  sulfate  solution.  The  values  given  in  the  tables  are  for  these 
amounts.  The  largest  result  obtained  in  the  series  was  that  with  pre- 
cipitated silica  when  the  concentration  of  copper  sulfate  was  0.000113 
gram  per  cc.  While  the  result  is  larger  than  any  of  those  obtained  using 
pearls  it  is  also  true  that  the  surface  exposed  is  enormously  larger.  This 
result,  therefore,  really  agrees  with  those  obtained  with  the  meshed  sands, 
all  of  them  indicating  that  the  adsorption  of  copper  from  copper  sulfate 
solution,  by  silica,  is  smaller  than  the  adsorption  of  the  same  substance 
by  glass. 

It  is  impossible,  from  the  results  obtained  to  give  a  definite  value  for 
the  adsorption  of  copper  by  glass.  The  amount  of  adsorption  varies  with 
the  concentration  of  the  copper  sulfate  solution,  and  also  with  the  size  of 
pearls  used.  The  variation  is  not  regular  for  either  concentration  or  pearl 
size. 

Results  were  obtained  using  six  different  concentrations  of  copper  sul- 
fate. For  the  most  part  the  results  show  good  agreement.  The  ad- 
sorption-time curves,  as  well  as  the  adsorption-concentration  curves,  ap- 
pear as  smooth  curves.  There  is  no  agreement  between  curves  represent- 
ing different  sizes  of  pearls,  however. 

Less  regularity  might  be  expected  for  the  thirty-minute  interval,  since 
this  represents  a  period  of  rapid  change  in  amount  adsorbed.  On  this 
account  curves  have  not  be  plotted  for  the  thirty-minute  period. 

In  the  work  done  on  adsorption  up  to  the  present  time,  only  a  single 
sized  grain  (usually  a  fine  powder  or  a  colloid)  has  been  used. l  With  this 

1  Z.  phys.  chem.,  57,  425  (1906);  Trans.  Lon.  Chem.  Soc.,  91-92,  1666  (1907); 
Biochem.  Z.,  23,  27-42  (1910);  Kolloid  Z.,  15,  10-18;  Z.  anorg.  Chem.,  60,  306-8  (1908); 
Compt.  rend.,  151,  72-5  (1911);  Proc.  Acad.  Wettenschappen,  15,  445-54  (1913). 


30 


Milligram  f  Adfortreet 
»  o,  §  5 

-  /  OH 

Z  60- 

Jl  01-U 
13  60-i 

a  wo  Son 

mtsh  Sa 
ltvo  San 
nesh  San 

ef-  Co/=t 
nd-Copp 
•j-Copp 
d-  Copfr 

*  PLATE  I 

Adso  rp  f/'o  n  -  Tim  e  Cur  ^ 

er  Cone.'  •  000042  a.  per  ce. 
er  Cone.  •=  .  oooi  /  3  tj.  per-  cc. 
er  Cone.  =.  ooo//3  cj.  per  cc. 
er  Cone.  =  .  000042  ej.  per  cc. 

res 

^ 

==r.= 

=.-r= 

i=^- 

~—  :jl 

««==-^=: 

L-r^: 

^4^-: 

fn(i- 

—  .a 

Time  in  hours 


PLATE  E 

Atfsorpf ''on-Time  Curves 
Sand  Samples 


Free.  Silica  -  Cu.  Cone. :  oew/3  a.  per  cc. 

Prtc.  Si  lie  a  Cu.  Cone.  * .  oeoo4z  q.  per  cc. 
4O-meshSai9a  Cu.  Cone.*. 000113  a.pir  cc. 
SO- mesh  Sand  Cu.  Cone.  -  .000113  ci.  per  cc. 
4o~mesh  Sandcu.  Cone.  *.  000042  2r.  per  cc. ' 
8O  mesh  Sand Cu.Conc.*.oooo4Zq.  per  cc. 


IS  20  25  30  35 

Time  in  hours 


I  Copper  Cone.  =  .oooess  a.  per  cc. 
2T  Copper  Cone.  =.OOS352  q.  pfr  cc. 
HI  Copper  Cone.  =.000153  q.  per  cc. 
IS  Copper  Cone.  =.ooo//3  <y.  per  cc. 
~S  Copper  Cone. -.OOCO4? cj.  fierce. 
Copper  Cone.  *.  OC/So  q.  Perec _ 


PLATE  M 

rption-  Time  Curves 
Pearls-  A/o.J. 


20  25  30 

Time  in  hours 


PL  Are  U 

Adsorption  -  Time 
Pearls  A/o.  3 


I  Copper  Conc.-.oooass  cj.  per  cc 
H  Copper  Cone.*. ooo3S2  a.  per  cc 

f  Copper  Conc.-.oooiS3  a.  per  cc. 
Copper  Conc.-.oooli3   a.  per  cc 
7  Copper  Conc.-.oooo41  $.  per  cc 
TI  Copper  Conc.z.ooiso  cj.  per  ec. 


25      _        30  35 

Time  in  hours 


material,  doubling  the  sample  doubles  the  adsorption  effect,  so  that  the 
amount  adsorbed  is  proportional  to  the  adsorbing  mass  or  surface  for  any 
one  concentration.  Since  the  pearl  samples,  using  different  sizes,  gave 
the  same  film  thickness  with  water,  it  was  expected  that  they  might  yield 
similar  results  with  copper,  that  is,  that  the  copper  adsorbed  would  be 
proportional  to  the  surface  exposed.  If  they  did  so,  it  would  eliminate 
mass  as  a  factor  in  adsorption.  If  they  did  not  do  so,  it  might  mean  either, 
that  varying  the  size  of  the  pearl  changed  the  amount  of  adsorption,  or 
that  the  adsorption  was  specific.  The  results  indicate  that  the  adsorption 
was  specific  since  no  relationship  has  been  found  between  the  amount  ad- 
sorbed and  the  total  surface,  or  between  the  amount  adsorbed  and  the  mass 
and  surface  of  the  individual  pearl  involved  in  the  adsorption.  This  still 
leaves  unsettled  the  question  as  to  whether  the  amount  adsorbed  varies 
with  the  mass  of  the  individual  particle  when  equal  adsorbing  surfaces 
are  used. 


I  Copper  Cone.  =jOOO6SS  q.  per  ec. 
»      H  Copper  Cone.  *.000352  q.  p*r  cc. 
7  Copper  Cone.  =.OOO/53  a-  per  cc. 


PLATE  V 


45  fO  •» 


PLAT£ 

Adsorption-  T/me  C 
Peat-Is  No.  7. 


CopperConc.  =.OOO65S  g.  per  cc. 

Copper  Cone.  *.OOO3S2  e}.  per  CC. 

Copper  Cone.  =.ooo/S3  a.  per  CC. 
JX  Copper  Cone.  *.000// 3  q.  per  CC. 
T  Copper  Conc.-.oooo^fZ  q.  per  cc, 
17  Copper  Cone.  =.  ooiSO  g.  per-  cc 


30  25  3O  35 

Time  in  hours 


\  | 


/  Copper  Cone.*  .COO6SSCJ.  percc, 
2T Copper  Cor.c.  =.000352 Cj.  per  cc. 
73  Copper  Conc.=.OOOI53Cf.  per  CC. 
jy  Copper  Cone.  —.GOOj/3  Cj.percc. 
Y  Copper  C&m:.  -.ooaotz  q.  percc. 
Q  50  .17 Copper  Cone.  -.OOiiO  q.  per  cc. 


PLATE 

Adsorption  -T 

Pearls  A/o.  d, 


Tims  in  hours 


The  curves  shown  on  Plates  I  to  IX  illustrate  the  change  in  adsorption 
with  time.  Almost  all  of  the  curves  are  typical  time-adsorption  curves 
if  the  effect  is  purely  physical.  The  adsorption  increases  immediately  to 
almost  its  maximum  value,  and  very  slightly  for  any  longer  period  of  time. 
A  few  of  the  curves  are  of  a  different  type,  a  considerably  longer  time  being 
required  to  reach  a  value  approximating  the  maximum,  and  a  gradual 
increase  in  adsorption  taking  place  throughout  the  whole  time  interval 
of  the  experiment.  These  curves  might  be  expected  if  a  chemical  reaction 


33 


Cone  =  .DOOSS.S  g.  per-  cc. 
fl  Copper  Cone  =.000352  q.  per  cc. 
M Copper  Cone  =.  CO/ SO  q.  per  cc. 


Time  in  hours 


$20 


— 

~ 

Ad 

~ 

PL  ATI 
sorpti 

—            1  IB          _ 

?  H 

on-Tin- 
Pear/ 

—  •'             ,_ 

?<?  Ccsr 
r  A/o.  A 
—  ? 

YtS 
2 

,.«•-•  

/ 

I 

V 

Copper  Cone. 
Copper  Cone. 
Copper  Cone. 

..  000655  g.  pet 
=  OO0153C).  per 
-  00  ISO  g.  per 

•  cc. 
cc. 

111 

cc. 

w 

K 

x  »- 

• 

/ 

5 

10             If             SO             25            30            35            4O           45            SO            &. 

Time  in  hours 

occurred  at  the  surface  of  contact.  The  velocity  of  reaction  would  be 
decreased  by  the  reaction  products  formed  especially  if  they  were  deposited 
on  the  glass,  so  that  a  considerable  time  might  be  required  to  reach  these 
maximum  values. 

It  can  be  stated  definitely  that  this  latter  type  of  curve  was  not  due  to 
an  impurity  on  the  surface  of  the  samples,  since  curves  obtained  after 
carefully  recleaning  the  pearls  were  of  the  same  shape,  the  magnitude  of 
the  individual  results  being  almost  the  same. 

Table  II  shows  the  adsorption  values  obtained  with  each  sample  of  pearls 
at  each  concentration  of  copper  sulfate  at  the  end  of  a  definite  period  of 
contact.  Consider  the  results  obtained  using  any  one  sample,  and  varying 
the  concentration  of  the  copper  sulfate  solution.  "M"  or  surface  is  con- 
stant. Therefore,  "X"  or  the  adsorbed  amount  should  vary  as  "C"  raised 
to  some  power  "n"  Under  these  conditions,  "X"  would  increase  as  "C" 
increases  if  'V  is  positive,  and  would  decrease  as  "C"  increases  if  "n" 
is  negative.  The  variation  in  the  value  of  "&"  is  the  only  factor  which 
would  interfere  with  this  relationship.  In  those  cases  in  which  the  value 
of  "k"  has  been  studied,1  to  determine  its  variation  with  the  concentra- 
1  Z.  Phys.  Chem.,  57,  425  (1906). 


34 


/  Pearls  /Vo.  7 

I  Pearls  A/o-3 

M  Pearls  No.  8 

UT Pearls  A/o./O 

Y  Pearls  A/o.  S 

F  Pearls  No.  I 
r/s 


tion,  very  little  variation  has  been  noticed,  and  none  that  would  ac- 
count for  the  adsorption  values  found.  "X,"  however,  does  not  show 
either  relationship. 

Taking  a  certain  concentration  of  copper  sulfate  solution  and  comparing 
the  values  obtained  with  each  of  the  pearl  samples  also  fails  to  show  any 
regularity.  If  equal  surfaces  of  the  different  pearl  samples  have  the  same 
capacity  to  adsorb  copper  sulfate,  as  they  do  for  a  water  film,  and  the  con- 
centration "C"  is  kept  constant  "X"  would  vary  as  "M."  "k"  and  "n" 
would  not  vary  if  the  nature  of  the  surface  is  the  same  and  the  concen- 
tration is  also  the  same.  The  results  do  not  show  any  relationship  be- 
tween "X"  and  "M." 

It  is  seen  from  what  has  preceded  that  there  is  no  fixed  amount  of  ad- 
sorption of  copper  from  solution,  by  glass,  but  that  the  amount  adsorbed 
varies  with  the  copper  concentration  and  with  the  size  of  the  pearls  used. 
It  is  also  seen  that  the  results  do  not  satisfy  the  adsorption  isotherm, 
which  requires  a  rapid  increase  in  amount  adsorbed  up  to  a  certain  concen- 
tration, and  a  very  gradual  increase  for  greater  concentrations.  All  of 
these  facts  indicate  that  we  are  not  dealing  with  an  ordinary  physical 
adsorption. 

The  values  given  in  Table  II  show  a  maximum  adsorption  for  one  of 
the  concentrations  used,  this  being  in  most  cases  the  concentration 
0.000655  gram  Cu  per  cc.  The  curves  showing  this  same  fact  are  shown 
on  Plates  X  and  XI.  While  the  curves  on  these  plates  are  drawn  as  con- 
tinuous curves,  it  should  be  stated  that  only  that  part  of  the  curve  to 
the  left  of  the  concentration,  0.000655  gram  per  cc.  has  been  fixed  by 


35 


/  Pearls  No.  7 

I  Pearls  Wo.  3. 

4s\-M  Pear/s  No. 3. 

H  Pearls  No.  10. 

7  Pearls  /V<j.  S. 

-  W  Pear/s  A/o.  I. 

JR  Pearls  No.  9. 


PLATE  H 

Adsorption  -Concentration  Curves 
(50  hrs.) 

Sv 


0.4  0.5  0.6  0.7  O.g 

Concentration  in  rnq  Cu 

adsorption  values  given  in  the  tables,  and  that  the  only  values  to  the 
right  of  this  concentration  are  those  for  the  concentration  0.00150  gram 
per  cc.  Consequently  the  part  of  the  curves  on  the  right  side  of  this  con- 
centration (0.000655)  may  not  have  the  shape  indicated.  The  values 
with  the  concentration  0.00150  gram  per  cc.  make  it  certain  that  the  ad- 
sorption value  does  decrease  at  some  point,  and  that  the  adsorption- 
concentration  curve  does  show  a  maximum. 

In  looking  through  the  literature  on  adsorption  it  was  found  that  several 
curves  of  this  kind  were  known,  and  that  these  adsorptions  which  showed 
a  maximum  value  for  a  given  concentration  were  classed  as  "anamolous."1 
In  fact  the  same  sort  of  an  effect  had  already  been  noticed  with  copper 
sulfate  when  it  is  adsorbed  by  filter  paper  or  clay.2  The  maximum  was 
obtained  with  a  0.02  N  solution,  corresponding  to  0.000638  gram  Cu  per 
cc. 

If  the  adsorption  is  purely  physical  there  are  three  possibilities  to  be 
considered.  Copper  sulfate,  undissociated,  may  be  adsorbed,  copper  ion 
may  be  adsorbed  or  copper  hydroxide  may  be  formed  by  hydrolysis  and 
absorbed.  If  the  adsorption  is  chemical,  a  reaction  between  copper 
sulfate  and  the  glass,  or  some  constituent  of  it,  would  result  in  copper  being 
deposited  on  the  glass  surface. 

The  percentage  dissociation  of  copper  sulfate  in  solution  for  the  con- 
centrations used,  can  be  calculated  from  the  conductivity  of  copper  sul- 

1  Zeit.  Chem.  Ind.  KolL,  7,  113-28;  9,  135-6;  Z.  Phys.  Chem.,  73,  399;  62,  655. 

2  J.  Phys.  Chem.,  10,  290-8  (1906). 


36 

fate  at  infinite  dilution  using  the  copper  and  the  sulfate  radical  (804), 
ionic  conductivities.1  The  dissociation  is  given  by  the  fraction,  \/\xt 
in  which,  \,  is  the  conductivity  at  the  dilution  used,  and  X^ ,  the  conduc- 
tivity at  infinite  dilution.  Very  probably  the  value  given  for  the  conduc- 
tivity at  the  greatest  dilution  (10,000  liters)  is  not  much  smaller  than  that 
at  infinite  dilution.  In  addition,  any  error  introduced  through  using  too 
small  a  value  for  X^  would  increase  the  percentage  dissociation  in  all 
cases  and  would  have  but  little  effect  on  the  relative  values. 

The  values  given  in  the  following  table  are  calculated  from  data  given 
in  Landolt-Bornstein's  Tabellen. 

TABLE  III. 
Dissociation  of  Copper  Sulfate  Solutions. 

Cu.  concentration  Dissociation  Weight  Cu  as  ion  ,       Weight  Cu  as 

grm.per  cc.  percent.  per  cc.  undis.  salt. 

0.000042  87.7  0.000037  0.000005 

O.OOOII3  78.4  0.000089  O.OOOO24 

0.000153          74-2          0.000113          0.000040 

0.000352  64.3  0.000226  0.000126 

0.000655  56.5  0.000370  0.000285 

0.00150  47-5  0.000612  0.000888 

It  is  readily  seen  from  this  table  that  the  aqtual  amount  of  copper  ion 
present  per  100  cc.  and  in  a  far  greater  measure,  the  actual  amount  of 
undissociated  copper  sulfate,  increases  with  the  concentration  of  the  copper 
sulfate  solution.  This  has  an  important  bearing  on  the  adsorption. 

If  the  copper  ion  were  adsorbed,  either  the  adsorption  should  increase 
in  some  proportion  as  the  amount  of  ion  present  increased,  or  it  should 
maintain  a  constant  value  above  a  certain  concentration  at  which  the 
surface  is  saturated  with  respect  to  the  adsorbed  substance.  That  is, 
a  normal  adsorption  curve  would  be  expected.  There  is  no  apparent  ex- 
planation for  an  adsorption-concentration  curve  of  the  kind  shown  on  the 
plates,  if  copper  ion  is  adsorbed.  The  same  is  true  if  copper  sulfate  un- 
dissociated, or  if  both  this  and  the  copper  ion  are  adsorbed. 

There  is,  however,  another  possibility,  without  the  necessity  of  con- 
sidering ions  or  compounds  not  known  to  exist  at  present.  Solutions  of 
copper  salts  are  known  to  react  acid.  This  can  be  explained  only  by  as- 
suming that  very  dilute  solutions  of  copper  sulfate  are  hydrolyzed,  ac- 
cording to  the  following  reactions : 

CuS04  Z£±  Cu++  +  S04=  T±   Cu(OH)2  +  H+  +  H+  +  SO4 

+  H+  +  H+  +  CT 
+  H+  +  H+  +  O" 

The  reactions  are  reversible  and  the  amount  of  undissociated  copper 
hydroxide  formed  depends  on  the  SO4  ion  present. 
1  Landolt-Bornstein  Tabellen,  p.  1103. 


37 

Table  III  gives  the  weight  of  copper  ion  per  cc.  at  each  concentration 
used,  from  which  the  weight  of  sulfate  ion  (SOJ  can  be  calculated.  It, 
of  course,  increases  in  the  same  proportion  as  the  weight  of  copper  ion. 

A  dilute  solution  of  copper  sulfate  may,  according  to  the  reaction  given 
above,  contain  undissociated  copper  sulfate,  copper  and  sulfate  ions,  and 
copper  hydroxide,  undissociated.  It  is  known  from  the  values  given  in 
Table  III  that  as  the  amount  of  copper  sulfate  per  liter  increases,  the  amount 
of  copper  ion  and  the  amount  of  sulfate  ion  both  increase,  although  the 
per  cent,  dissociation  decreases.  It  might  be  expected  that,  at  least  for 
the  lower  concentrations,  the  amount  of  copper  hydroxide  per  cc.  would 
also  increase. 

However  the  formation  of  copper  hydroxide  differs  from  that  of  copper 
ion.  That  is,  different  forces  are  active  in  determining  the  amounts  of 
the  two  substances  present.  The  copper  ion  formed  is  dependent  on  the 
amount  of  copper  sulfate  dissolved,  and  increases  in  the  same  proportion 
as  the  sulfate  ion  does.  The  copper  hydroxide  formed  also  depends  in  a 
measure,  on  the  copper  sulfate  dissolved,  and  on  the  relative  amounts  of 
the  ions  present.  As  the  reaction  shows  it  is  in  equilibrium  with  the 
sulfate  ion.  Consequently  at  some  concentration,  the  amount  of  sulfate 
ion  in  solution  will  become  great  enough  so  that  no  copper  hydroxide  can 
exist,  and  the  equation  representing  the  solution  of  the  salt  will  become: 
CuS04^±Cu++  +  S04= 

According  to  this  assumption  the  amount  of  copper  hydroxide  present 
in  a  dilute  solution  of  copper  sulfate,  increases  as  the  concentration  of  the 
salt  increases,  up  to  a  certain  point  at  which  the  amount  of  sulfate  ion 
present,  is  great  enough  to  cause  a  part  of  the  copper  hydroxide  to  dissolve. 
Above  this  concentration  the  amount  of  copper  hydroxide  decreases  as 
the  concentration  increases. 

It  will  be  noted  that  the  adsorption-concentration  curves  show  the  same 
characteristics.  The  amount  of  copper  adsorbed  increases  with  the  con- 
centration of  the  sulfate,  up  to  a  certain  concentration.  Above  this  con- 
centration the  amount  of  copper  adsorbed  decreases,  being  very  close  to 
zero  at  the  highest  concentration  used  (0.00150  g.  Cu  per  cc.). 

It  has  been  impossible  to  get  any  definite  data  on  the  amount  of  copper 
hydroxide  present  in  these  solutions.  A  maximum  is  obtained,  however, 
in  the  adsorption-concentration  curves,  and  a  similar  maximum  may  be 
expected  in  the  curve  showing  the  change  in  concentration  of  copper 
hydroxide  as  the  concentration  of  copper  sulfate  increases.  If  it  is  as- 
sumed that  the  adsorption-concentration  curve  is  dependent  on  the  copper 
hydroxide  concentration  curve,  the  shape  of  the  adsorption  curve  would 
correspond  to  that  found  experimentally.  No  other  satisfactory  expla- 
nation has  been  given.  Likewise,  if  copper  hydroxide  is  adsorbed  and  the 


38 

curves  are  plotted  using  the  concentration  of  copper  sulfate  as  abscissae, 
an  ordinary  adsorption  curve  would  not  be  expected. 

It  is  possible,  therefore,  to  explain  the  results  obtained  on  the  assump- 
tion that  hydrolysis  of  copper  sulfate  takes  place  in  dilute  solution,  with 
the  formation  of  undissociated  copper  hydroxide,  copper  hydroxide  being 
adsorbed.  This  would  permit  of  viewing  the  adsorption  as  purely  physical 
in  its  nature. 

It  might  also  be  stated  that  the  same  sort  of  an  explanation  would 
apply  to  all  of  the  cases  of  "anamolous  adsorption"  found  in  the  literature. 
This  type  of  curve  is  limited  definitely  to  inorganic  salts  and  to  basic  dyes, 
both  of  which  are  apt  to  be  subject  to  hydrolytic  dissociation. 

It  seems  probable  that  only  a  slight  amount  of  hydrolysis  takes  place 
with  any  of  the  concentrations  used.  Only  one  statement  was  found  for 
the  amount  of  hydrolysis  of  copper  sulfate  solution,  and  the  volume  em- 
ployed is  questionable  in  that  case.  The  per  cent,  hydrolysis  shown  was 
0.057  per  cent.1 

According  to  the  explanation  given  for  the  shape  of  the  adsorption- 
concentration  curve,  this  adsorption  must  be  physical  in  its  nature  con- 
sisting in  a  concentration  of  undissociated  copper  hydroxide  on  the  sur- 
face of  the  glass  pearls. 

The  fact  that  no  surface  relationship  was  found  is  the  strongest  indica- 
tion that  the  adsorption  is  not  physical.  Whether  the  substance  actually 
adsorbed  is  copper  sulfate,  copper  ion  or  copper  hydroxide,  doubling  the 
surface  exposed  should  double  the  amount  adsorbed,  if  the  adsorption  is 
physical.  On  the  other  hand,  if  the  curve  results  from  a  chemical  reac- 
tion occurring  at  the  surface  of  the  glass  pearls,  it  is  difficult  to  under- 
stand why  increasing  the  concentration  of  copper  sulfate  decreases  the 
amount  of  copper  adsorbed. 

The  explantion  given  for  the  type  of  curve  obtained  is  satisfactory  for 
the  results  found  experimentally.  It  requires  that  we  assume  that  copper 
hydroxide  is  adsorbed.  While  this  seems  probable,  and  while  it  serves 
to  explain  the  fact  that  a  peculiar  type  of  curve  is  obtained  in  this  adsorp- 
tion, the  adsorption  of  copper  hydroxide  could  not  be  shown  experimentally. 

Summary. 

1.  This  paper  deals  with  the  adsorption  of  copper  from  copper  sulfate 
solution  by  glass  and  sand. 

2.  The  concentration-adsorption  curves  show  maximum  values  and  do 
not  correspond  with  the  ordinary  adsorption  curves. 

3.  No  relationship  was  found  to  exist  between  the  total  surface  exposed 
and  the  amount  adsorbed. 

1  Landolt-Bornstein  Tabellen,  p.  1190. 


39 

4.  An  explanation  is  given  based  on  the  assumption  that  adsorption  of 
copper  hydroxide,   formed  by  hydrolysis,   occurs.     The  adsorption  be- 
longs to  the  class  of  adsorptions  known  as  "anamolous  adsorptions." 

5.  The  adsorption  is  considered  to  be  physical  in  its  nature,  although 
the  results  do  not  definitely  prove  this  point. 


PART  III.— THE  ADSORPTION  OF  IODINE  BY  STARCH. 

Introduction. — In  the  two  previous  papers  of  this  series  adsorption  values 
were  obtained  for  the  adsorption  of  a  liquid  by  glass  and  for  the  adsorp- 
tion of  a  solute  by  glass.  In  the  first  case  several  liquids  were  used  as 
adsorbed  substance  and  in  the  latter,  water  was  used  as  the  solvent  and 
copper  sulfate  as  the  solute.  In  the  present  paper  values  are  presented 
for  the  adsorption  of  a  solute  from  an  organic  solvent.  Values  are  also 
given  for  the  adsorption  of  the  vapor  of  the  organic  solvent,  the  vapor 
of  the  solute  and  the  vapor  of  the  solution. 

Curves  for  pure  vapor  adsorptions  are  fairly  numerous,  as  are  those 
for  solutes  in  water  solution.  For  the  most  part  they  are  of  the  type  of 
ordinary  adsorption  curves.  Some  work  has  also  been  done  on  adsorp- 
tion from  organic  solvents,  notable  that  by  Freundlich.1  The  effect  of 
a  solute  which  is  volatile  on  the  adsorption  of  the  vapors  of  the  solvent 
has  not  been  determined.  It  may  be  considered  as  the  adsorption  of 
mixed  vapors,  and  may  be  expected  to  give  values  which  are  specific  for 
the  substances  used  and  also  in  a  measure  dependent  on  the  vapor  pressure 
of  the  solvent. 

Materials. 

Adsorbed  Substance. — Iodine  seemed  best  fitted  for  the  purpose  of  this 
investigation.  In  the  solid  state  its  vapor  pressure  is  slight  but  greater 
than  that  of  most  solids.  Solutions  could  readily  be  made  of  it  in  almost 
any  organic  liquid,  and  it  could  be  determined  easily  and  accurately. 
In  addition  it  was  known  to  be  strongly  adsorbed  by  starch,  the  solid 
finally  chosen  in  this  piece  of  work,  for  adsorption  purposes. 

Solvents. — Three  organic  liquids  were  chosen  as  solvents  for  the  iodine, 
these  being  alcohol,  acetic  acid  and  nitrobenzene.  Alcohol  has  a  relatively 
high  vapor  pressure,  that  of  acetic  acid  is  considerably  smaller,  and  nitro- 
benzene has  a  vapor  pressure  of  less  than  i  mm.  at  ordinary  tempera- 
tures. It  was  hoped  that  results  with  these  three  liquids  would  serve  to 
determine  whether  the  vapor  pressure  of  the  solvent  played  any  part  in 
determining  the  amount  of  the  adsorbed  vapor. 
1  Z.  Phys.  Chem.,  57,  385  (1906). 


40 

A  tenth  normal  solution  of  iodine  in  each  of  these  solvents  was  prepared, 
the  resublimed  iodine  being  weighed  into  a  glass  stoppered  weighing  bottle 
and  the  stoppered  bottle  being  dropped  into  a  measured  volume  of  the 
solvent.  After  the  iodine  had  dissolved  the  solution  was  transferred  to 
a  flask  and  additional  solvent  added  to  make  the  solution  tenth  normal. 
The  actual  amount  of  iodine  present  was  checked  by  titrating  a  known 
volume  of  the  solution  with  standardized  solution  of  sodium  thiosulfate. 

Adsorbing  Substance. — It  was  originally  intended  to  use  the  glass  pearls 
described  in  the  previous  papers  as  the  adsorbing  solid,  in  order  to  carry 
out  the  work  with  known  surfaces.  In  an  attempt  to  determine  the  amount 
of  adsorption  that  might  be  expected,  a  preliminary  set  of  determinations 
was  run  using  a  3o-gram  sample  of  precipitated  silica.  The  results  ob- 
tained were  positive  in  every  case,  indicating  an  adsorption,  but  were  very 
small  in  amount.  Since  even  smaller  results  might  be  expected  with  the 
glass  pearls,  it  was  decided  that  some  other  adsorbing  medium  was  re- 
quired, and  that  the  surface  factor  could  only  be  roughly  controlled. 

Starch  was,  therefore,  substituted  for  the  pearls.  The  starch  made  use 
of  was  coarsely  ground  so  that  it  would  pass  a  twenty-mesh  sieve  but 
would  be  held  on  one  of  forty  mesh.  It  was  dried  at  110°  for  three  hours 
previous  to  use. 

Method. 

1.  Adsorption  of  Vapors  of  Pure  Solvent  and  Pure  Solute. — Fifty  cubic 
centimeters  of  one  of  the  organic  liquids  was  placed  in  the  bottom  of  a 
five-inch  desiccator  having  a  tight  fitting  cover.     Supported  above  the 
liquid  was  a  glass  stoppered  weighing  flask  (open)  containing  a  gram  of 
the  starch.     At  intervals  the  glass  stoppered  flask  was  capped,  wiped  dry, 
removed  from  the  desiccator,  let  stand  for  an  hour  in  the  balance  case 
and  weighed.     It  was  then  replaced  and  the  weighing  continued.     Weigh- 
ings were  made  in  the  same  way  using  each  of  the  pure  organic  liquids  and 
also  pure  iodine. 

2.  Adsorption  from  Solution. — Five  grams  of  the  starch  described  above 
was  transferred  to  a  2oo-ce.  flask.     One  hundred  cc.  of  a  tenth-normal 
solution  of  iodine  was  poured  over  it.     The  flask  was  closed  with  a  ground 
glass  stopper  and  well  shaken.     At  the  time  intervals  noted  in  the  tables, 
lo-cc.  portions  were  pipetted  off  with  a  carefully  calibrated  pipette  and 
the  iodine  present  determined.    This  series  was  run  with  each  of  the  iodine 
solutions. 

3.  Adsorption  from  Vapors  of  Tenth-Normal  Solutions. — The  same 
apparatus  and  the  same  procedure  was  used  for  this  series  of  determina- 
tions was  used  for  the  adsorptions  of  the  vapors  of  the  pure  solvents. 
One  gram  of  starch  was  used  for  each  determination. 


The  work  was  all  done  without  the  use  of  a  thermostat  Temperature 
readings  taken  at  intervals  did  not  indicate  a  temperature  variation  of 
more  than  two  degrees. 

TABLE  I. 
Vapors  Adsorbed  by  i  G.  Starch  from  Pure  Solvent  and  Pure  Solute. 


Time  in  hrs. 

Nitrobenzene. 

Time  in  hrs. 

Alcohol. 

Acetic  acid- 

Iodine. 

23 

O.OOOI 

16 

0.0290 

o  .  0976 

0.0379 

47 

0.0016 

64 

0.0295 

0.1025 

o  .  0448 

71 

0.0018 

88 

0.0300 

o.  1040 

o  .  0448 

96 

0.0038 

112 

0.0313 

0.0447 

120 

0.0058 

136 

0.0311 

O.IOSI 

0.0448 

192 

0.0108 

.... 

.... 

.... 

240 

0.0140 

.... 

.... 

II. 

Vapors  Adsorbed  by  i  G.  Starch  from  N/io  Solutions. 

2       0.0073               0.0079  0.0182 

6       0.0085                ....  0.0220 

24       0.0172               0.0228  0.0596 

48       0.0235               0.0485  0.1019 

72       0.0309               0.0671  0.1305 

96       0.0421                ....  0.1492 

240       0.1064               0.0906  0.1969 

TABLE  III. 
Vapors  Adsorbed  by  i  G.  Starch  from  Vapors  of  N/io  Solutions. 


24 

O.OOO4 

16 

0.0371 

0.1073 

48 

0.0034 

64 

o  .  0392 

o.  1140 

72 

0.0052 

88 

0.0406 

0.1155 

96 

o  .  0085 

112 

o  .  0425 

120 

O.OIlS 

136 

0.0440 

0.1250 

192 

O.O2O6 

.... 

.... 

240 

O.O27O 

.... 

Discussion  of  Results. — As  noted  above  the  temperature  varied  some- 
what during  the  course  of  these  experiments.  The  effect  of  this  tempera- 
ture variation  would  be  a  slight  change  in  the  vapor  pressure  of  the  liquid 
in  use.  It  would  be  entirely  negligible  in  the  case  of  nitrobenzene  and 
iodine.  This  change  in  vapor  pressure  has  been  considered  to  have  a 
negligible  effect  upon  the  amount  of  adsorption  in  all  of  the  cases  studied. 

i.  Curves  for  Pure  Solvent  and  Pure  Solute. — The  curves  in  this  series 
are  of  two  types.  Alcohol,  acetic  acid  and  iodine  vapors  show  time  curves 
that  are  typical  for  adsorptions.  They  rise  within  a  relatively  short  time 
to  about  the  maximum  value  and  the  adsorption  increases  gradually  with 
time  beyond  that  point  over  the  whole  period  of  the  experiment.  Alcohol 
vapor  shows  the  least  adsorption,  iodine  vapor  the  mean,  and  acetic  acid 
vapor  the  maximum  adsorption. 


Adsorption  from  &  Iodine  Solutions 


lAceb'cAdd  Solution 
I  Nitrobenzene  Solution 
IE  Alcohol  Solution 


ZO  40  60  30  100  IZO  140  /6O  ISO  ZOO  ZZO  Z4Q 


. 

• 

w 

PLATL 

•E 

.3 

\ 

I  Vapors  of  Iodine 
I  VaporsofZ  Solutior 
IH  Vapors  of  Pure  Mtn 

£ 

^benzol 

/ 

/ 

•- 

AM 

^ 

rf 

x' 

^ 

^ 

^ 

^ 

^ 

^ 

^ 

^ 

M 

,^* 

^ 

"^ 

^ 

^^ 

^--' 

L 

^^ 

_^~- 

^^ 
*•" 

^* 

—  *^ 

20           40            60            00            100           ISO           140           160          180          ZOO          220         240 

Time  in  hours 


One  of  the  objects  of  this  series  of  experiments  was  to  determine  whether 
vapor  pressure  was  an  important  factor  in  determining  the  adsorbed  amount 
or  whether  the  adsorption  was  specific  for  the  liquid  used,  and  only  de- 
pendent on  vapor  pressure  insofar  as  it  supplies  vapor  for  adsorption. 


43 


.130 
.120 
.110 
.100 


.090 


.080 


\.010 


.030 

.020\ 

.010 


L 


L 


UT 


I  Vapors  of  fa  Solution  oflodini 
fl  Vapors  of  Pure  Acetic  Acid 
H  Vapors  of  Iodine 


20  40  60  80  100          l?0          140 

Time  in  hours 


I  Vapors  of  %  Solution 
W  fabors  of  Purf  A/cohol 


10  20  30  40  SO  fO  70  80  90  ISO 


44 

This  has  been  determined  by  these  experiments.  The  vapor  pressure  of 
alcohol  is  44  mm.  at  20°  C.,  that  of  acetic  acid,  1 1.7  mm.  and  that  of  iodine 
only  a  fraction  of  a  millimeter.  Since  the  amounts  adsorbed  are  not 
proportional  to  these  vapor  pressures  the  conclusion  must  be  drawn  that 
the  adsorbed  amount  depends  principally  upon  the  specific  affinity  of  the 
starch  for  the  vapors,  and  only  to  a  slight  extent,  if  at  all,  upon  the  actual 
amount  of  vapor  present  during  the  adsorption. 

For  nitrobenzene  the  adsorption-time  curve  is  a  straight  line.  In  this 
case  the  liquid  has  a  vapor  pressure  of  only  a  fraction  of  a  millimeter. 

2.  Curves  for  Adsorption  from  Tenth-Normal  Solutions. — The  curves 
for  the  adsorption  of  iodine  from  tenth  normal  solutions  are  similar  to 
those  for  adsorption  of  the  vapors  of  the  corresponding  pure  solvent, 
though  they  fail  to  show  an  equally  sharp  bend  to  the  horizontal.     This 
is  due  to  the  fact  that  adsorption  and  absorption  took  place  at  the  same 
time  from  the  solution.     In  this  case  also  the  curve  for  nitrobenzene  is 
practically  a  straight  line. 

It  may  be  noted  that  the  curve  is  the  same  for  the  three  solutions  as  it 
is  for  the  vapors  of  the  corresponding  pure  liquids,  and  that  the  magni- 
tude of  the  results  is  in  the  same  order  as  before,  i.  e.,  acetic  acid  gives  the 
largest  adsorption  values,  alcohol  the  next  largest  and  nitrobenzene  the 
smallest  values. 

3.  Curves  for  Vapors  of  Tenth-Normal  Solutions. — Vapors  from  tenth- 
normal  solutions  in  acetic  acid,  in  alcohol  and  in  nitrobenzene  give  curves 
which  correspond  closely  to  those  obtained  with  vapors  of  the  correspond- 
ing solutes.     In  each  case,  however,  the  addition  of  the  iodine  has  increased 
the  amount  of  the  adsorption,  the  increase  being  about  50%  in  the  case 
of  nitrobenzene,  26%  in  the  case  on  alcohol,  and  only  10%  in  the  case  of 
acetic  acid.     The  increase  measured  in  grams  is,  however,  in  the  same 
order,  as  the  rest  of  the  results,  being  greatest  for  acetic  acid  and  least  for 
nitrobenzene. 

Dissolving  iodine  in  the  organic  solvents  would  lower  the  vapor  pressure 
of  the  liquid.  This  would,  since  it  decreases  the  concentration  of  the  vapor 
phase,  decrease  the  amount  of  the  vapor  present.  It  is  found,  however, 
that  the  amount  of  adsorption  is  greater  when  the  vapor  of  the  solution  is 
adsorbed  than  when  the  vapor  of  the  pure  solvent  is  adsorbed.  This  in- 
crease is  due  to  the  adsorption  of  iodine  vapor. 

No  data  are  available  for  the  vapor  pressure  of  iodine  or  for  the  vapor 
pressure  of  the  solute  in  tenth  normal  solution,  so  that  the  concentrations 
cannot  be  calculated.  The  results  indicate  that  the  adsorption  would  be 
independent  of  the  concentration  of  the  vapors  of  iodine  and  solvent,  so 
that  determining  them  would  not  assist  in  interpreting  the  results  obtained. 


45 

The  starch  assumed  a  light  blue  color  when  standing  over  the  solution  which 
proves  that  iodine  was  adsorbed.  Its  amount,  however,  was  not  de- 
termined. 

The  adsorption  of  the  vapors  of  organic  solvents  and  of  iodine  depend 
upon  the  specific  affinity  of  starch  for  these  substances  and  is  not  de- 
pendent on  any  physical  properties  common  to  the  adsorbed  substances. 


This  investigation  was  undertaken  at  the  suggestion  of  Dr.  I.  H.  Derby. 
I  take  this  opportunity  of  expressing  my  sincerest  thanks  for  his  guidance 
and  advice. 


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